macio: switch over to new byte-aligned DMA helpers

Now that the DMA helpers are byte-aligned they can be called directly from
the macio routines rather than emulating byte-aligned accesses via multiple
block-level accesses.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-Id: 1476445266-27503-3-git-send-email-mark.cave-ayland@ilande.co.uk
Signed-off-by: John Snow <jsnow@redhat.com>