romfs: have romfs_fs.h pull in necessary headers

This header uses things like __be32, so pull in linux/types.h.

Further, it uses BLOCK_SIZE, so pull in linux/fs.h.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>