LU-16518 utils: fix unused function errors

LU-16518 utils: fix unused function errors

Clang has default errors related to unused functions.
The errors related to 'fid_flatten' and 'fid_flatten32'
were resolved by moving the definitions of these
functions to the 'lustre_fid' header. This is a better
place for them, since they are small 'static inline'
functions and has the added benefit of cutting down
code duplication.

The error related to the 'static inline' function
'list_replace_init' was resolved by moving it to
'ofd_access_batch.h'.

The userspace implementation of 'fid_hash' has been
moved to the 'lustreapi.h' header.

Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I9714a2f36910c871c0a4579cf9400cb9ba72ec27
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/49901
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>