vga: disable global_vmstate, virtio-gpu scanout tracking fixes.

# gpg: Signature made Tue 03 Jul 2018 10:44:56 BST
# gpg:                using RSA key 4CB6D8EED3E87138
# 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>"
# Primary key fingerprint: A032 8CFF B93A 17A7 9901  FE7D 4CB6 D8EE D3E8 7138

* remotes/kraxel/tags/vga-20180703-pull-request:
  vga: disable global_vmstate for 3.0+ machine types
  virtio-gpu: disable scanout when backing resource is destroyed
  virtio-gpu: update old resource too.
  virtio-gpu: tweak scanout disable.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

# Conflicts:
#	hw/display/qxl.c
#	hw/display/vga-isa-mm.c