drm/udl: add cache flags definitions for udl_gem_object
By default set udl_gem_object as cacheable, but set WC flag when attaching
dmabuf. In udl_gem_mmap() update cache attributes based on the flags, similar
to exynos_drm_gem_mmap().
Signed-off-by: Haixia Shi <hshi@chromium.org> Reviewed-by: Sonny Rao <sonnyrao@chromium.org> Reviewed-by: Olof Johansson <olofj@chromium.org> Reviewed-by: Stéphane Marchesin <marcheu@chromium.org> Signed-off-by: Dave Airlie <airlied@redhat.com>