drm/amdkfd: add Van Gogh KFD support

This patch is to add GFX10 based APU Van Gogh KFD support. We will treat Van
Gogh as "dgpu" (bypass IOMMU v2).

Signed-off-by: Huang Rui <ray.huang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Yong Zhao <Yong.Zhao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>