mac_scsi: Convert to platform device

Convert mac_scsi to platform device and eliminate scsi_register().

Platform resources for chip registers now follow the documentation. This
should fix issues with the Mac IIci (and possibly other models too).

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>