[SCSI] gdth: split out isa probing

(note: this is ontop of Jeff's pci cleanup patch)

Split out isa probing into a helper of it's own.  Error handling is
cleaned up, but errors are not propagated yet.  Also enclose the isa
probe under the proper CONFIG_ISA symbol instead of the !IA64 hack.
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>