virtio-gpu: bugfixes and spice support preparation

# gpg: Signature made Wed 03 Feb 2016 09:47:13 GMT using RSA key ID D3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>"
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>"
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>"

* remotes/kraxel/tags/pull-vga-20160203-1:
  virtio-gpu: block any rendering until client (ui) is done
  virtio-gpu: add support to enable/disable command processing
  virtio-gpu: maintain command queue
  virtio-gpu: fix memory leak in error path
  console: block rendering until client is done
  zap qemu_egl_has_ext in include/ui/egl-helpers.h
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>