rp2pio: Add pins_are_sequential

This can be used where the standard API calls for a list of pins, to check that they satisfy the requirements of the rp2pio state machine, e.g.,
```python
    def __init__(self, pin_a, pin_b):
        if not rp2pio.pins_are_sequential([pin_a, pin_b]):
            raise ValueError("Pins must be sequential")
```

ports/raspberrypi/bindings/rp2pio/__init__.c

@@ -28,13 +28,28 @@
 #include "py/runtime.h"
 
 #include "bindings/rp2pio/StateMachine.h"
+#include "bindings/rp2pio/__init__.h"
 
 //| """Hardware interface to RP2 series' programmable IO (PIO) peripheral."""
 //|
 
+//| def pins_are_sequential(pins: List[microcontroller.Pin]) -> bool:
+//|     """Return True if the pins have sequential GPIO numbers, False otherwise"""
+//|     ...
+//|
+STATIC mp_obj_t rp2pio_pins_are_sequential(const mp_obj_t pins) {
+    size_t len;
+    mp_obj_t *items;
+    mp_obj_get_array(pins, &len, &items);
+    return mp_obj_new_bool(common_hal_rp2pio_pins_are_sequential(len, items));
+}
+
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(rp2pio_pins_are_sequential_obj, rp2pio_pins_are_sequential);
+
 STATIC const mp_rom_map_elem_t rp2pio_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_rp2pio) },
     { MP_ROM_QSTR(MP_QSTR_StateMachine),  MP_ROM_PTR(&rp2pio_statemachine_type) },
+    { MP_ROM_QSTR(MP_QSTR_pins_are_sequential),  MP_ROM_PTR(&rp2pio_pins_are_sequential_obj) },
 };
 
 STATIC MP_DEFINE_CONST_DICT(rp2pio_module_globals, rp2pio_module_globals_table);

ports/raspberrypi/bindings/rp2pio/__init__.h

@@ -0,0 +1,29 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2021 Jeff Epler for Adafruit Industries
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#pragma once
+
+bool common_hal_rp2pio_pins_are_sequential(size_t len, mp_obj_t *items);

ports/raspberrypi/common-hal/rp2pio/__init__.c

@@ -1 +1,43 @@
-// Nothing yet.
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2021 Jeff Epler for Adafruit Industries
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "py/obj.h"
+#include "shared-bindings/microcontroller/Pin.h"
+#include "bindings/rp2pio/__init__.h"
+
+bool common_hal_rp2pio_pins_are_sequential(size_t len, mp_obj_t *items) {
+    if(len == 0) {
+        return true;
+    }
+    mcu_pin_obj_t *last_pin = validate_obj_is_pin(items[0]);
+    for(int i=1; i<len; i++) {
+        mcu_pin_obj_t *pin = validate_obj_is_pin(items[i]);
+        if (pin->number != last_pin->number + 1) {
+            return false;
+        }
+    }
+    return true;
+}