libata: implement ATA_FLAG_IGN_SIMPLEX and use it in sata_uli

Some uli controllers have stuck SIMPLEX bit which can't be cleared
with ata_pci_clear_simplex(), but the controller is capable of doing
DMAs on both channels simultaneously.  Implement ATA_FLAG_IGN_SIMPLEX
which makes libata ignore the simplex bit and use it in sata_uli.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

include/linux/libata.h

@@ -177,6 +177,7 @@ enum {
 					      * Register FIS clearing BSY */
 	ATA_FLAG_DEBUGMSG	= (1 << 13),
 	ATA_FLAG_SETXFER_POLLING= (1 << 14), /* use polling for SETXFER */
+	ATA_FLAG_IGN_SIMPLEX	= (1 << 15), /* ignore SIMPLEX */
 
 	/* The following flag belongs to ap->pflags but is kept in
 	 * ap->flags because it's referenced in many LLDs and will be