bugfixes for qemu (bochs, qxl and virtio-gpu) drm drivers

* tag 'drm-qemu-20160921' of git://git.kraxel.org/linux:
  drm/virtio: add real fence context and seqno
  drm/virtio: drop virtio_gpu_execbuffer_ioctl() wrapping
  virtio-gpu: avoid possible NULL pointer dereference
  drm/qxl: reapply cursor after SetCrtc calls
  bochs: ignore device if there isn't enougth memory