Fill voltage fields in metrics table

v2: Removed dpm and freq ranges info
v3: Added check to ensure volrage offset is not zero
Signed-off-by: David M Nieto <david.nieto@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>