vga: add vhost-user-gpu.

# gpg: Signature made Wed 29 May 2019 05:40:02 BST
# gpg:                using RSA key 4CB6D8EED3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>" [full]
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>" [full]
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>" [full]
# Primary key fingerprint: A032 8CFF B93A 17A7 9901  FE7D 4CB6 D8EE D3E8 7138

* remotes/kraxel/tags/vga-20190529-pull-request:
  hw/display: add vhost-user-vga & gpu-pci
  virtio-gpu: split virtio-gpu-pci & virtio-vga
  virtio-gpu: split virtio-gpu, introduce virtio-gpu-base
  spice-app: fix running when !CONFIG_OPENGL
  contrib: add vhost-user-gpu
  util: compile drm.o on posix
  virtio-gpu: add a pixman helper header
  virtio-gpu: add bswap helpers header
  vhost-user: add vhost_user_gpu_set_socket()
  virtio-gpu: add sanity check

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>