fat: restructure export operations

fat: restructure export operations

Define two nfs export_operation structures,one for 'stale_rw' mounts and
the other for 'nostale_ro'.The former uses the generic export_encode_fh
function to encode file handle, while the latter uses fat_encode_fh().

Since inode number is not needed for nostale_ro, remove it from struct
fat_fid and repack other needed info viz.  i_pos and i_generation.

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Ravishankar N <ravi.n1@samsung.com>
Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.com>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>