drm/virtio: implement context init: track {ring_idx, emit_fence_info} in virtio_gpu_fence

drm/virtio: implement context init: track {ring_idx, emit_fence_info} in virtio_gpu_fence

Each fence should be associated with a [fence ID, fence_context,
seqno].  The seqno number is just the fence id.

To get the fence context, we add the ring_idx to the 3D context's
base_fence_ctx.  The ring_idx is between 0 and 31, inclusive.

Each 3D context will have it's own base_fence_ctx. The ring_idx will
be emitted to host userspace, when emit_fence_info is true.

Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
Acked-by: Lingfeng Yang <lfy@google.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20210921232024.817-7-gurchetansingh@chromium.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>