xfs_io: make statx mask parsing more generally useful

xfs_io: make statx mask parsing more generally useful

Enhance the statx -m parsing to be more useful:

Add words for all the new STATX_* field flags added in the previous
patch.

Allow "+" and "-" prefixes to add or remove flags from the mask.

Allow multiple arguments to be specified as a comma separated list.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Andrey Albershteyn <aalbersh@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>