f2fs: detect wrong layout

commit 2040fce83fe17763b07c97c1f691da2bb85e4135 upstream.

Previous mkfs.f2fs allows small partition inappropriately, so f2fs should detect
that as well.

Refer this in f2fs-tools.

mkfs.f2fs: detect small partition by overprovision ratio and # of segments

Reported-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>