csky: dtb Kbuild fixup patches for linux-4.20-rc1 These patches are complementary to "C-SKY(csky) Port for Linux 4.20" and fixup dtb Kbuild to follow the new Devicetree dtb build rules. Link: https://lore.kernel.org/lkml/CABGGisxiWaQn9qDqpfxEWcckkGJfMzFvSPGvuhQK7oB404-6DQ@mail.gmail.com/ Signed-off-by: Guo Ren <ren_guo@c-sky.com>