i965: Implement INTEL_performance_query backend

i965: Implement INTEL_performance_query backend

This adds a bare-bones backend for the INTEL_performance_query extension
that exposes pipeline statistics.

Although this could be considered redundant given that the same
statistics are already available via query objects, they are a simple
starting point for this extension and it's expected to be convenient for
tools wanting to have a single go to api to introspect what performance
counters are available, along with names, descriptions and semantic/data
types.

This code is derived from Kenneth Graunke's work, temporarily removed
while the frontend and backend interface were reworked.

Signed-off-by: Robert Bragg <robert@sixbynine.org>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>