drm/amdgpu: Update MMHUB power gating register settings

The new register settings are needed to fix a tlb invalidation issue
when MMHUB power gating is turned on for Raven.

Signed-off-by: Yong Zhao <yong.zhao@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Eric Huang <JinhuiEric.Huang@amd.com>
Reviewed-by: Eric Huang <JinhuiEric.Huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>