drm/amdgpu/swsmu: add metrics enums for voltage

To be used in subsequent patches.
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>

drivers/gpu/drm/amd/pm/inc/amdgpu_smu.h

@@ -613,6 +613,8 @@ typedef enum {
 	METRICS_TEMPERATURE_VRMEM,
 	METRICS_THROTTLER_STATUS,
 	METRICS_CURR_FANSPEED,
+	METRICS_VOLTAGE_VDDSOC,
+	METRICS_VOLTAGE_VDDGFX,
 } MetricsMember_t;
 
 enum smu_cmn2asic_mapping_type {