drm/amd/display: Enable VM support only on APUs newer than CZ

VM support is only available for CZ and newer APUs. Trying to
enable it for dGPU will blow up in DC.

v2: Don't enable gpu_vm_support for Raven yet since it leads to
    a black screen. Need to debug this further before enabling.

Change-Id: Ibe467c36affe2e7a7ee740c8d4f73027ca807178
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Suggested-by: Alex Deucher <alexander.deucher@amd.com>
CC: Christian Koenig <christian.koenig@amd.com>
Reviewed-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>