anv: add a fake compute queue support
We can make up fake queues by creating another GEM context and make it look like another queue.
This was useful to debug timeline semaphore CTS test cases that would not normally run on our implementation because we only support a single queue.
We're also curious to know whether this could help apps in a situation where a single queue is a bottleneck.
Run your app with ANV_FAKE_COMPUTE_QUEUE=1 ./my_vk_app
Signed-off-by: Lionel Landwerlin email@example.com