drm/amdgpu: Refactor mode2 reset logic for v11.0.7

- refactor mode2 on v11.0.7 to align with aldebaran
- comment out using mode2 reset as default for now, will introduce
another controller to replace previous reset_level_mask

v2: squash in unused variable removal (Alex)

Signed-off-by: Victor Zhao <Victor.Zhao@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>