scsi: build scsi_common.o for all scsi passthrough request users

Split scsi_common.o out of SCSI so that non-SCSI users can pull it in
easily for future sense buffer helper usage.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>