anv/query: Busy-wait for available query entries

anv/query: Busy-wait for available query entries

Before, we were just looking at whether or not the user wanted us to
wait and waiting on the BO.  Some clients, such as the Serious engine,
use a single query pool for hundreds of individual query results where
the writes for those queries may be split across several command
buffers.  In this scenario, the individual query we're looking for may
become available long before the BO is idle so waiting on the query pool
BO to be finished is wasteful. This commit makes us instead busy-loop on
each query until it's available.

This significantly reduces pipeline bubbles and improves performance of
The Talos Principle on medium settings (where the GPU isn't overloaded
with drawing) by around 20% on my SkyLake gt4.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Eero Tamminen <eero.t.tamminen@intel.com>
Tested-by: Grazvydas Ignotas <notasas@gmail.com>