drm/amd/powerplay: keep soft_pp_table pointer value for re-uploading

Necessary for updating pptables at runtime.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Eric Huang <JinHuiEric.Huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>