drm/amdgpu/discovery: enable gmc v11 for GC 11.0.4

Enable gmc (graphic memory controller) v11 for GC 11.0.4.

Signed-off-by: Yifan Zhang <yifan1.zhang@amd.com>
Reviewed-by: Aaron Liu <aaron.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>