drm/virtio: Support sync objects

Add sync object DRM UAPI support to VirtIO-GPU driver. Sync objects
support is needed by native context VirtIO-GPU Mesa drivers, it also will
be used by Venus and Virgl contexts.

Reviewed-by; Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Tested-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com> # amdgpu nctx
Tested-by: Rob Clark <robdclark@gmail.com> # freedreno nctx
Reviewed-by: Rob Clark <robdclark@gmail.com>
Acked-by: Gurchetan Singh <gurchetansingh@chromium.org>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230416115237.798604-4-dmitry.osipenko@collabora.com