drm/qxl: use generic fbdev emulation

Switch qxl over to the new generic fbdev emulation.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20190118122020.27596-18-kraxel@redhat.com