drm/amdgpu: fall back to INPUT power for AVG power via INFO IOCTL

For backwards compatibility with userspace.

Fixes: 47f1724d ("drm/amd: Introduce `AMDGPU_PP_SENSOR_GPU_INPUT_POWER`")
Link: drm/amd#2897


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