nv50,nvc0: stop limiting the number of active queries to 1

nv50,nvc0: stop limiting the number of active queries to 1

This limitation was initially here because AMD_performance_monitor
doesn't allow to expose the real number of hardware counters. But
this actually really annoying when profiling with qapitrace.

Anyways, performance counters are mostly for developers and
failures are expected if you try to monitor more queries than
supported.

This breaks amd_performance_monitor_measure but it's expected.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>