Remove the Kbuild rules in arch/csky and use common dtb build rules.
This modification is based on:
commit 37c8a5fafa ("kbuild: consolidate Devicetree dtb build rules")
Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>