xfs: remove __psint_t and __psunsigned_t

Replace uses of __psint_t with the proper uintptr_t and ptrdiff_t types,
and remove the defintions of __psint_t and __psunsigned_t.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>