drm/amd/powerplay: Update SMU firmware loading for Stoney

Fix firmware init on Stoney when powerplay is enabled.

Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>