[SCSI] gdth: switch to modern scsi host registration

  - Use scsi_add_host and friends and track instances ourselves. And
    generally modernize the driver's structure.

  - TODO: Next we can remove the controller table
  - TODO: Fix use of deprecated pci_find_device()

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>