drm/amd/pm: Vangogh: Get average_* from average field of gpu_metrics_table

for older BIOS, smu won't fill average field of gpu_metrics_table, so we acquire
average_* from current field. but now average value is available in gpu_metrics_v2_4

Signed-off-by: Kun Liu <Kun.Liu2@amd.com>
Acked-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>