[PATCH] libata CHS: calculate read/write commands and protocol on the fly (revise #6)

     - 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: Albert Lee <albertcc@tw.ibm.com>

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