esp32: Change from FAT to littlefs v2 as default filesystem.

This commit changes the default filesystem type for esp32 to littlefs v2.
This port already enables both VfsFat and VfsLfs2, so either can be used
for the filesystem, and existing systems that use FAT will still work.
import uos
from flashbdev import bdev


def check_bootsec():
    buf = bytearray(bdev.ioctl(5, 0))  # 5 is SEC_SIZE
    bdev.readblocks(0, buf)
    empty = True
    for b in buf:
        if b != 0xFF:
            empty = False
            break
    if empty:
        return True
    fs_corrupted()


def fs_corrupted():
    import time

    while 1:
        print(
            """\
FAT filesystem appears to be corrupted. If you had important data there, you
may want to make a flash snapshot to try to recover it. Otherwise, perform
factory reprogramming of MicroPython firmware (completely erase flash, followed
by firmware programming).
"""
        )
        time.sleep(3)


def setup():
    check_bootsec()
    print("Performing initial setup")
    uos.VfsLfs2.mkfs(bdev)
    vfs = uos.VfsLfs2(bdev)
    uos.mount(vfs, "/")
    with open("boot.py", "w") as f:
        f.write(
            """\
# This file is executed on every boot (including wake-boot from deepsleep)
#import esp
#esp.osdebug(None)
#import webrepl
#webrepl.start()
"""
        )
    return vfs

import uos
from flashbdev import bdev


def check_bootsec():
    buf = bytearray(bdev.ioctl(5, 0))  # 5 is SEC_SIZE
    bdev.readblocks(0, buf)
    empty = True
    for b in buf:
        if b != 0xFF:
            empty = False
            break
    if empty:
        return True
    fs_corrupted()


def fs_corrupted():
    import time

    while 1:
        print(
            """\
FAT filesystem appears to be corrupted. If you had important data there, you
may want to make a flash snapshot to try to recover it. Otherwise, perform
factory reprogramming of MicroPython firmware (completely erase flash, followed
by firmware programming).
"""
        )
        time.sleep(3)


def setup():
    check_bootsec()
    print("Performing initial setup")
    uos.VfsFat.mkfs(bdev)
    vfs = uos.VfsFat(bdev)
    uos.mount(vfs, "/")
    with open("boot.py", "w") as f:
        f.write(
            """\
# This file is executed on every boot (including wake-boot from deepsleep)
#import esp
#esp.osdebug(None)
#import webrepl
#webrepl.start()
"""
        )
    return vfs
