xfs: remove ATTR_ALLOC and XFS_DA_OP_ALLOCVAL

xfs: remove ATTR_ALLOC and XFS_DA_OP_ALLOCVAL

Use a NULL args->value as the indicator to lazily allocate a buffer
instead, and let the caller always free args->value instead of
duplicating the cleanup.

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Dave Chinner <[email protected]>
Reviewed-by: Chandan Rajendra <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Signed-off-by: Darrick J. Wong <[email protected]>