libata: move sas ata tag allocation to libata-scsi.c

Basically move the sas ata tag allocation to libata-scsi.c to make it clear
these staffs are just for sas.

Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
3 files changed