drm/amdgpu/swsmu/vangogh: use metrics table for voltages (v2)

Fixes voltage reading for vddgfx and adds support for vddsoc.

v2: use new voltage enum

Reviewed-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>