[PATCH] libata-hp: implement ata_eh_detach_dev()

Implement ata_eh_detach_dev().  This function is responsible for
detaching an ATA device and offlining the associated SCSI device
atomically so that the detached device is not accessed after ATA
detach is complete.

Signed-off-by: Tejun Heo <htejun@gmail.com>