drm/amdgpu: add vcn 4.0.6 discovery support

This patch is to add vcn 4.0.6 support

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