LU-17848 osd: move fid_is_fs_root() to lustre_fid.h

LU-17848 osd: move fid_is_fs_root() to lustre_fid.h

Move the duplicate fid_is_fs_root() functions to the
lustre_fid.h header.

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I43d914dc28cf653deb0fa48228877c9dae503383
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/57743
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>