drm/amdgpu: add NBIO IP v7.7.0 Clock Gating support

Add BIF Clock Gating MGCG and LS support for NBIO IP v7.7.0.

Signed-off-by: Tim Huang <tim.huang@amd.com>
Reviewed-by: Yifan Zhang <yifan1.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>