[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 <brking@us.ibm.com>

(with slight merge modifications made by...)
Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 6b3c3af..20b1cf5 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -483,6 +483,7 @@
 struct ata_port {
 	struct Scsi_Host	*host;	/* our co-allocated scsi host */
 	const struct ata_port_operations *ops;
+	spinlock_t		*lock;
 	unsigned long		flags;	/* ATA_FLAG_xxx */
 	unsigned int		id;	/* unique id req'd by scsi midlyr */
 	unsigned int		port_no; /* unique port #; from zero */