[XFS] Add op_flags field and helpers to xfs_da_args
The end of the xfs_da_args structure has 4 unsigned char fields for
true/false information on directory and attr operations using the
xfs_da_args structure.
The following converts these 4 into a op_flags field that uses the first 4
bits for these fields and allows expansion for future operation
information (eg. case-insensitive lookup request).