This commit adds support for littlefs (v2) on all esp32 boards.
The original FAT filesystem still works and any board with a preexisting
FAT filesystem will still work as normal. It's possible to switch to
littlefs by reformatting the block device using:
import uos, flashbdev
uos.VfsLfs2.mkfs(flashbdev.bdev)
Then when the board reboots (soft or hard) the new littlefs filesystem will
be mounted. It's possible to switch back to a FAT filesystem by formatting
with uos.VfsFat.mkfs(flashbdev.bdev).
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