drm/amdgpu/smu: add helper function smu_get_dpm_level_range() for smu driver

this function can help smu driver to query dpm level clock range from
smu firmware.

Signed-off-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>