GPU frequency can be included in the trace by adding the ftrace category.
data_sources: {
    config {
        name: "linux.ftrace"
        ftrace_config {
            ftrace_events: "power/gpu_frequency"
        }
    }
}
GPU counters can be configured by adding the data source to the trace config as follows:
data_sources: {
    config {
        name: "gpu.counters"
        gpu_counter_config {
          counter_period_ns: 1000000
          counter_ids: 1
          counter_ids: 3
          counter_ids: 106
          counter_ids: 107
          counter_ids: 109
        }
    }
}
The counter_ids correspond to the ones described in GpuCounterSpec in the data source descriptor.
See the full configuration options in gpu_counter_config.proto