mesa/glthread: add glthread "perf" counters and pass them to gallium HUD

for HUD integration in following commits. This valuable profiling data
will allow us to see on the HUD how well glthread is able to utilize
parallelism. This is better than benchmarking, because you can see
exactly what's happening and you don't have to be CPU-bound.

u_threaded_context has the same counters.

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/mesa/main/glthread.h

@@ -65,6 +65,9 @@ struct glthread_state
    /** Multithreaded queue. */
    struct util_queue queue;
 
+   /** This is sent to the driver for framebuffer overlay / HUD. */
+   struct util_queue_monitoring stats;
+
    /** The ring of batches in memory. */
    struct glthread_batch batches[MARSHAL_MAX_BATCHES];