drm/amdgpu: Use wafl version for xgmi

XGMI and WAFL share the same versions. Use WAFL version if XGMI version
is not present in discovery.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Asad Kamal <asad.kamal@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>