ANDROID: drm/virtio: plumb {base_fence_ctx, fence_ctx_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>

BUG: 173630595
TEST: boot VM

Change-Id: I4c305a663af3986dd952ebef09564d6648961fc8