ata: add CONFIG_SATA_HOST=n version of ata_ncq_enabled()

When CONFIG_SATA_HOST=n there are no NCQ capable host drivers
built so it is safe to hardwire ata_ncq_enabled() to always
return zero.

Code size savings on m68k arch using (modified) atari_defconfig:

   text    data     bss     dec     hex filename
before:
  37820     572      40   38432    9620 drivers/ata/libata-core.o
  21040     105     576   21721    54d9 drivers/ata/libata-scsi.o
  17405      18       0   17423    440f drivers/ata/libata-eh.o
after:
  37582     572      40   38194    9532 drivers/ata/libata-core.o
  20702     105     576   21383    5387 drivers/ata/libata-scsi.o
  17353      18       0   17371    43db drivers/ata/libata-eh.o
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/libata.h

@@ -1633,6 +1633,8 @@ extern struct ata_device *ata_dev_next(struct ata_device *dev,
  */
 static inline int ata_ncq_enabled(struct ata_device *dev)
 {
+	if (!IS_ENABLED(CONFIG_SATA_HOST))
+		return 0;
 	return (dev->flags & (ATA_DFLAG_PIO | ATA_DFLAG_NCQ_OFF |
 			      ATA_DFLAG_NCQ)) == ATA_DFLAG_NCQ;
 }