Add JPEG support

[sfe-SparkFro]

JPEG support had to be disabled to implement imread() and imwrite() #4 (comment):

micropython-opencv/src/opencv/platforms/common.cmake

Lines 21 to 22 in 8f16324

	set(WITH_JPEG OFF)
	set(WITH_OPENJPEG OFF)

When it's enabled, building for RP2350 results in the following linker error:

undefined reference to `posix_memalign'