s390/qdio: clean up QDR setup

__qdio_allocate_fill_qdr() is meant to set up one specific queue
descriptor in the QDR. But for this simple task, it gets passed a bunch
of global structs and offsets - and then navigates through the structs
to find its actual operands.

Clean up all the complicated pointer chasing & index calculation, and
just pass a descriptor and its associated queue struct.

While at it also add some virt_to_phys() translations, to clarify that
addresses in the QDR are meant to be absolute.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>