Add local copies of ata_id_string() and ata_id_c_string() to mg_disk
so there is no need for the driver to depend on ATA and SCSI.

[ Impact: break dependency on libata by copying ata id string functions ]

Cc: unsik Kim <donari75@gmail.com>
Signed-off-by: NBartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>