mesa: Separate INTEL_performance_query frontend

mesa: Separate INTEL_performance_query frontend

To allow the backend interfaces for AMD_performance_monitor and
INTEL_performance_query to evolve independently based on the more
specific requirements of each extension this starts by separating
the frontends of these extensions.

Even though there wasn't much tying these frontends together, this
separation intentionally copies what few helpers/utilities that were
shared between the two extensions, avoiding any re-factoring specific to
INTEL_performance_query so that the evolution will be easier to follow
later.

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