drm/amdgpu: init nbio v7_9 callbacks

switch to the new nbio generation for NBIO 7.9.0.

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Le Ma <Le.Ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>