mali_kbase: platform: dvfs: Clean up metrics

All changes to clock and power state are now reported to the metrics
logic via a single function: gpu_dvfs_metrics_update(). This
function tracks clock and power stats as well as issuing tracepoints
for frequency changes.

Signed-off-by: Sidath Senanayake <sidaths@google.com>
Change-Id: I94d789eca3cc626fdbbbd4eb2c9dbeac7fe489e1