Move dce_virtual into amdgpu_vkms and update all references to
dce_virtual with amdgpu_vkms.

v2: Removed more references to dce_virtual.

v3: Restored display modes from previous implementation.
Signed-off-by: Ryan Taylor <Ryan.Taylor@amd.com>
Reported-by: kernel test robot <lkp@intel.com>
Suggested-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>