virgl: make resource_wait/resource_is_busy cheaper

virgl: make resource_wait/resource_is_busy cheaper

The round trip to the kernel is expensive.  Add a local cache to
avoid it when possible.

There is a race condition when two contexts access the same resource
at the same time (e.g., ctx1 submits a cmdbuf that accesses a
resource while ctx2 maps the resource).  But that is probably an app
bug in the first place.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>