qxl: add sanity check to make sure we aren't back in VGA mode.
qxl: add sanity check to make sure we aren't back in VGA mode.

For some reason we still sometimes end up back in VGA mode,
I suspect a kernel VGA access somewhere while under KD_GRAPHICS,
on real HW it would ignore this, qxl seems to "unique" and not
in a good way.

dezelin/xf86-video-qxl,fgouget/xf86-video-qxl,facboy/xserver-xorg-video-qxl,sombrafam/virtioqxl-xf86-video-qxl,facboy/xserver-xorg-video-qxl,dezelin/xf86-video-qxl,fgouget/xf86-video-qxl,facboy/xserver-xorg-video-qxl,sombrafam/virtioqxl-xf86-video-qxl,fgouget/xf86-video-qxl,sombrafam/virtioqxl-xf86-video-qxl,dezelin/xf86-video-qxl,facboy/xserver-xorg-video-qxl,fgouget/xf86-video-qxl