MIPS: JZ4740: Add Kbuild files

Add the Kbuild files for the JZ4740 architecture and adds JZ4740 support
to the MIPS Kbuild files.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/1406/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>