Add frequency setting for RP2040 boards.

ports/raspberrypi/Makefile

@@ -229,6 +229,7 @@ SRC_SDK := \
 	src/rp2_common/pico_printf/printf.c \
 	src/rp2_common/pico_runtime/runtime.c \
 	src/rp2_common/pico_stdio/stdio.c \
+	src/rp2_common/pico_stdlib/stdlib.c \
 	src/rp2_common/pico_unique_id/unique_id.c \
 	$(SRC_SDK_CYW43) \
 

ports/raspberrypi/common-hal/microcontroller/Processor.c

@@ -28,10 +28,12 @@
 #include <string.h>
 
 #include "py/mphal.h"
+#include "py/runtime.h"
 #include "common-hal/microcontroller/Processor.h"
 #include "shared-bindings/microcontroller/Processor.h"
 #include "shared-bindings/microcontroller/ResetReason.h"
 
+#include "pico/stdlib.h"
 #include "src/rp2_common/hardware_adc/include/hardware/adc.h"
 #include "src/rp2_common/hardware_clocks/include/hardware/clocks.h"
 
@@ -59,6 +61,16 @@ uint32_t common_hal_mcu_processor_get_frequency(void) {
     return clock_get_hz(clk_sys);
 }
 
+uint32_t common_hal_mcu_processor_set_frequency(mcu_processor_obj_t *self,
+    uint32_t frequency) {
+    uint32_t freq = frequency / 1000;
+
+    if (!set_sys_clock_khz(freq, false)) {
+        mp_raise_ValueError(translate("Invalid frequency supplied"));
+    }
+    return clock_get_hz(clk_sys);
+}
+
 void common_hal_mcu_processor_get_uid(uint8_t raw_id[]) {
     pico_unique_board_id_t retrieved_id;
     pico_get_unique_board_id(&retrieved_id);

ports/raspberrypi/mpconfigport.mk

@@ -48,3 +48,4 @@ CIRCUITPY_BUILD_EXTENSIONS ?= uf2
 USB_NUM_ENDPOINT_PAIRS = 8
 
 INTERNAL_FLASH_FILESYSTEM = 1
+CIRCUITPY_SETTABLE_PROCESSOR_FREQUENCY = 1

shared-bindings/microcontroller/Processor.c

@@ -67,7 +67,7 @@
 //|     frequency: int
 //|     """The CPU operating frequency in Hertz.
 //|
-//|     **Limitations:** Setting the ``frequency`` is possible only on some i.MX boards.
+//|     **Limitations:** Setting the ``frequency`` is possible on RP2040 boards and some i.MX boards.
 //|     On most boards, ``frequency`` is read-only.
 //|     """