drm/amd/powerplay: move the function of read_sensor to asic file

The read_sensor functions has asic related parts code,
so move them to asic file to implement.

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