drm/amdgpu/nv: add mode2 reset handling

Vangogh will use mode2 reset, so plumb it through the nv
soc driver.

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