drm/amd/powerplay: add interface to get current clocks for display

This patch fills the amd_pp_clock_info data for display, it will get the current
info in that structure.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Kevin Wang <Kevin1.Wang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>