drm/amd/powerplay: revise default dpm tables setup

Initialize the soft/hard min/max level correctly and
handle the dpm disabled situation.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>