xpenology: Enable SAS support for synology.

- SAS drives now use normal SATA style addresses
- Additional debuging information added to help troubleshooting naming issues
xpenology: XenVBD devices should be seend as scsi devices

- Added XENVBD_MAJOR to switch statement
xpenology: XenVBD kernel param support for SCSI driver.

- Included access to the new global kernel param g_xen_vbd_devices
- Used g_xen_vbd_device to offset the want_idx for drives when being mapped
xpenology: XenVBD count kernel parameter support.

- Enabled access to global g_xen_vbd_devices
- Used g_xen_vbd_device to offset the drive want_idx value
xpenology: More debug code to track drive index issues