vdsm: add support for ram/vram on QXL device

setting support for qxl device with proper ram/vram attributes:

1 Monitor, Single PCI checked     64MB   32MB
2 Monitors, Single PCI checked    128MB  32MB
4 Monitors, Single PCI checked    256MB  32MB

Change-Id: I71cc51acf22dbce66373009f0c6ec8e2022a4f87
Bug-Url: https://bugzilla.redhat.com/787578
Signed-off-by: Shahar Havivi <shaharh@redhat.com>
Signed-off-by: Vinzenz Feenstra <vfeenstr@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/19361
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>
Tested-by: Martin Betak <mbetak@redhat.com>
Reviewed-by: Martin Polednik <mpoledni@redhat.com>
Reviewed-by: Saggi Mizrahi <smizrahi@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>