drm/amdgpu/powerplay:avoid to show invalid DPM table info

for different ASIC support different the number of DPM levels,
we should avoid to show the invalid level value.
v1 -> v2:
	follow the suggestion,clarifiy the description for this
change

Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Yuxian Dai <Yuxian.Dai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>