libata: Implement control mode page to select sense format

Implement MODE SELECT for the control mode page to allow the OS
to switch to descriptor sense.

tj: Dropped s/sb/cmd->sense_buffer/ in ata_gen_ata_sense().  Added
    @dev description to ata_msense_ctl_mode().

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 2c4ebef..a418bca 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -180,6 +180,7 @@
 	ATA_DFLAG_DA		= (1 << 26), /* device supports Device Attention */
 	ATA_DFLAG_DEVSLP	= (1 << 27), /* device supports Device Sleep */
 	ATA_DFLAG_ACPI_DISABLED = (1 << 28), /* ACPI for the device is disabled */
+	ATA_DFLAG_D_SENSE	= (1 << 29), /* Descriptor sense requested */
 
 	ATA_DEV_UNKNOWN		= 0,	/* unknown device */
 	ATA_DEV_ATA		= 1,	/* ATA device */