amd_performance_monitor: give driver some time before giving up
Currently, the "measure" test depends on one of these possibilities:
- the counters it selects are computed by the driver on the CPU side, so they can be returned immediately
- asking for hardware counters value is extremely fast (in order of microseconds)
- the driver blocks waiting for hardware counters (unlikely)
- the CPU is very slow (unlikely for x86_64)
For Iris we currently hit 1), but if we change the order of counters (something I would like to do) Iris will fail because of 2).
On my SKL system asking for HW counters take ~10ms, so 5 x 50ms in this test should be enough even for a heavily loaded system.