drm/virtio: implement context init: plumb {base_fence_ctx, ring_idx} to virtio_gpu_fe...

drm/virtio: implement context init: plumb {base_fence_ctx, ring_idx} to virtio_gpu_fence_alloc

These were defined in the previous commit. We'll need these
parameters when allocating a dma_fence.  The use case for this
is multiple synchronizations timelines.

The maximum number of timelines per 3D instance will be 32. Usually,
only 2 are needed -- one for CPU commands, and another for GPU
commands.

As such, we'll need to specify these parameters when allocating a
dma_fence.

vgdev->fence_drv.context is the "default" fence context for 2D mode
and old userspace.

Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
Acked-by: Lingfeng Yang <lfy@google.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20210921232024.817-8-gurchetansingh@chromium.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>