[SCSI] gdth: split out pci probing

Split out per-device pci probing and put it under proper CONFIG_PCI.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>