ata: start separating SATA specific code from libata-scsi.c

ata: start separating SATA specific code from libata-scsi.c

Start separating SATA specific code from libata-scsi.c:

* un-static ata_scsi_find_dev()

* move following code to libata-sata.c:
  - SATA only sysfs device attributes handling
  - __ata_change_queue_depth()
  - ata_scsi_change_queue_depth()

* cover with CONFIG_SATA_HOST ifdef SATA only sysfs device
  attributes handling code and ATA_SHT_NCQ() macro in
  <linux/libata.h>

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

   text    data     bss     dec     hex filename
before:
  20702     105     576   21383    5387 drivers/ata/libata-scsi.o
after:
  19137      23     576   19736    4d18 drivers/ata/libata-scsi.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>