drm/amdgpu: add syncobj create/destroy/import/export apis

These are just wrappers using the amdgpu device handle.

Acked-by: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>