drm/i915/gvt: add VFIO EDID region

Implement VFIO EDID region for vgpu. Support EDID blob update and notify
guest on link state change via hotplug event.

v3: move struct edid_region to kvmgt.c <zhenyu>
v2: add EDID sanity check and size update <zhenyu>

Tested-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Hang Yuan <hang.yuan@linux.intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>