drm/powerplay: Fix Vega20 Average Power value v4

The SMU changed reading from CurrSocketPower to AverageSocketPower, so
reflect this accordingly. This fixes the issue where Average Power
Consumption was being reported as 0 from SMU 40.46-onward

v2: Fixed headline prefix
v3: Add check for SMU version for proper compatibility
v4: Style fix

Signed-off-by: Kent Russell <kent.russell@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>