f2fs: Support Block Size == Page Size

This allows f2fs to support cases where the block size = page size for
both 4K and 16K block sizes. Other sizes should work as well, should the
need arise. This does not currently support 4K Block size filesystems if
the page size is 16K.

Signed-off-by: Daniel Rosenberg <drosen@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>