[libata] Add host lock to struct ata_port

Prepare for changes required to support SATA devices
attached to SAS HBAs. For these devices we don't want to
use host_set at all, since libata will not be the owner
of struct scsi_host.

Signed-off-by: Brian King <[email protected]>

(with slight merge modifications made by...)
Signed-off-by: Jeff Garzik <[email protected]>
5 files changed