drm/amdgpu/discovery: enable gmc v11 for GC 11.0.1

Enable gmc (graphic memory controller) v11 for GC 11.0.1.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Aaron Liu <aaron.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>