fat: add extended fileds to struct fat_boot_sector

Later we will need "state" field to check if volume was cleanly unmounted.

Signed-off-by: Oleksij Rempel <bug-track@fisher-privat.net>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>