Create OpenCV Board Variants

[sfe-SparkFro]

Because OpenCV adds ~3MB to the firmware size, any ports that require the storage size to be manually specified (eg. rp2) need to have variants defined that reduce the storage size to avoid it overlapping with the firmware (causes all kinds of fun problems!).

The current automated firmware build doesn't handle this properly. I have some local changes that fix this, which should be committed to the public MicroPython repo closer to launch, in case it catches attention.

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For example, with the XRP Controller, create mpconfigvariant_OPENCV.cmake:

list(APPEND MICROPY_DEF_BOARD
    # Board name
    "MICROPY_HW_BOARD_NAME=\"SparkFun XRP Controller (OpenCV)\""
    # 8MB (8 * 1024 * 1024)
    "MICROPY_HW_FLASH_STORAGE_BYTES=8388608"
)

Then add #ifndef wrappers in mpconfigboard.h for MICROPY_HW_BOARD_NAME and MICROPY_HW_FLASH_STORAGE_BYTES so the variant can build properly.

---

After board variants have been defined, Makefile should have the following added:

# Ensure we're building the OpenCV board variant
MAKE_ARGS += BOARD_VARIANT=OPENCV

And under clean: and submodules:, $(MAKE_ARGS) should be added so the correct directory is selected for those operations.

[sfe-SparkFro]

Could also address this at the same time with a board variant:

micropython-opencv/src/alloc.c

Lines 4 to 11 in ca68e8c

	// Hacky solution to see if the GC is initialized. If so, we can use gc_alloc
	// and gc_free. Otherwise, we need to use __real_malloc and __real_free.
	// TODO: Determine if this is acceptable or if we should use a different method.
	// Would be nice to be able to #define MICROPY_BOARD_EARLY_INIT to set a flag,
	// however that needs to be #defined in the board's mpconfigboard.h file.
	bool gc_inited() {
	return MP_STATE_MEM(area).gc_pool_start != NULL;
	}

[sfe-SparkFro]

d9501a7 implements a temporary solution that obfuscates the naming. Should rename from "large binary" to "OpenCV" for launch. Should also pick a more precise value for the storage size, 8MB was arbitrary.

[sfe-SparkFro]

Done in sparkfun/micropython@e23e46a