RFC libata: support SATA devices on SAS HBAs

The following patches enhance libata to allow SAS device drivers to utilize libata to talk to SATA devices. It introduces some new APIs which allow libata to be used without allocating a virtual scsi host. This is just a snapshot of what I've come up with at this point and I figured I would post it to see if I was heading in a reasonable direction or not, so don't expect the code below to do anything useful at this point as it is untested.

New APIs:

ata_sas_port_alloc - Allocate an ata_port
ata_sas_port_init - Initialize an ata_port (probe bus, etc) ata_sas_port_destroy - Free an ata_port allocated by ata_sas_port_alloc ata_sas_slave_configure - configure scsi device ata_sas_queuecmd - queue a scsi command, similar to ata_scsi_queuecomand

These new APIs can be used either directly by a SAS LLDD or could be used by the SAS transport class.

Possible usage for a SAS LLDD would be:

scsi_scan_host
slave_alloc
ata_sas_port_alloc
ata_sas_port_init
slave_configure
ata_sas_slave_configure

Commands received by the LLDD for SATA devices would call ata_sas_queuecmd.

Device teardown would occur with:

slave_destroy
ata_sas_port_destroy

Brian King
eServer Storage I/O
IBM Linux Technology Center