wd719x: Introduce Western Digital WD7193/7197/7296 PCI SCSI card driver

Introduce wd719x, a driver for Western Digital WD7193, WD7197 and WD7296 PCI
SCSI controllers based on WD33C296A chip.
Tested with WD7193 card.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>