Automatically count EXTERNAL_FLASH_DEVICES (mk2)

Instead of counting words in make, which is slightly awful, notice that
possible_devices is local to external_flash.c, so we can declare the array
with an automatic bound, and then get the count as the element-count
(MP_ARRAY_SIZE) of the array.

Since EXTERNAL_FLASH_DEVICE_COUNT is no longer a global macro, switch
a few sites to using EXTERNAL_FLASH_DEVICES in `#if` checks instead.

supervisor/flash.h

@@ -31,7 +31,7 @@
 
 #include "py/mpconfig.h"
 
-#ifdef EXTERNAL_FLASH_DEVICE_COUNT
+#ifdef EXTERNAL_FLASH_DEVICES
 #include "supervisor/shared/external_flash/external_flash.h"
 #else
 #include "supervisor/shared/internal_flash.h"

supervisor/flash_root_pointers.h

@@ -26,7 +26,7 @@
 #ifndef MICROPY_INCLUDED_SUPERVISOR_FLASH_ROOT_POINTERS_H
 #define MICROPY_INCLUDED_SUPERVISOR_FLASH_ROOT_POINTERS_H
 
-#ifdef EXTERNAL_FLASH_DEVICE_COUNT
+#ifdef EXTERNAL_FLASH_DEVICES
 #include "supervisor/shared/external_flash/external_flash_root_pointers.h"
 #else
 #include "supervisor/internal_flash_root_pointers.h"

supervisor/shared/external_flash/external_flash.c

@@ -45,7 +45,8 @@
 // The currently cached sector in the cache, ram or flash based.
 static uint32_t current_sector;
 
-const external_flash_device possible_devices[EXTERNAL_FLASH_DEVICE_COUNT] = {EXTERNAL_FLASH_DEVICES};
+STATIC const external_flash_device possible_devices[] = {EXTERNAL_FLASH_DEVICES};
+#define EXTERNAL_FLASH_DEVICE_COUNT MP_ARRAY_SIZE(possible_devices)
 
 static const external_flash_device* flash_device = NULL;
 

supervisor/supervisor.mk

@@ -33,10 +33,7 @@ endif
 # (Right now INTERNAL_FLASH_FILESYSTEM and (Q)SPI_FLASH_FILESYSTEM are mutually exclusive.
 # But that might not be true in the future.)
 ifdef EXTERNAL_FLASH_DEVICES
-  COMMA := ,
-  EXTERNAL_FLASH_DEVICE_COUNT := $(words $(subst $(COMMA), ,$(EXTERNAL_FLASH_DEVICES)))
   CFLAGS += -DEXTERNAL_FLASH_DEVICES=$(EXTERNAL_FLASH_DEVICES) \
-	    -DEXTERNAL_FLASH_DEVICE_COUNT=$(EXTERNAL_FLASH_DEVICE_COUNT)
 
   SRC_SUPERVISOR += supervisor/shared/external_flash/external_flash.c
     ifeq ($(SPI_FLASH_FILESYSTEM),1)