pc-bios/s390-ccw: Get list of supported VPD pages

The "Supported Pages" Inquiry EVPD page is mandatory for all SCSI devices,
and is used as a gateway for what VPD pages the device actually supports.
Let's issue this Inquiry, and dump that list with the debug facility.

Signed-off-by: Eric Farman <farman@linux.vnet.ibm.com>
Message-Id: <20170510155359.32727-6-farman@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>