drm/amdgpu: skip kfd init if GFX is not ready.

avoid kfd init crash in that case.

Signed-off-by: Yifan Zhang <yifan1.zhang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Tested-by: Jesse Zhang <Jesse.Zhang@amd.com>
Reviewed-by: Jesse Zhang <Jesse.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>