virgl: rework queries

virgl: rework queries

virglrender has been changed such that

 - VIRGL_CCMD_GET_QUERY_RESULT is fenced
 - query buffers (PIPE_BIND_CUSTOM) are coherent

We can check if a query is ready using DRM_IOCTL_VIRTGPU_WAIT, and also
avoid a synchronized transfer to retrieve the query result.  When
running against an older virglrenderer, it falls back to the old
behavior automatically.

TF2 @ 640x480 for pts4.dem went from 17fps to 40fps on my testing
machine.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>