- merge ata_prot_to_cmd() and ata_dev_set_protocol() as
       ata_rwcmd_protocol()
     - pave road for read/write multiple support
     - remove usage of pre-cached command and protocol values and call
       ata_rwcmd_protocol() instead
Signed-off-by: NAlbert Lee <albertcc@tw.ibm.com>

==============
Signed-off-by: NJeff Garzik <jgarzik@pobox.com>