MIPS: Ingenic: Add Ingenic X1000 support.

Support the Ingenic X1000 SoC using the code under arch/mips/jz4740.
This is left unselectable in Kconfig until a X1000 based board is
added in a later commit.

Signed-off-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@wanyeetech.com>
Signed-off-by: Paul Burton <paulburton@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: devicetree@vger.kernel.org
Cc: robh+dt@kernel.org
Cc: paul.burton@mips.com
Cc: jhogan@kernel.org
Cc: mripard@kernel.org
Cc: shawnguo@kernel.org
Cc: mark.rutland@arm.com
Cc: alexandre.belloni@bootlin.com
Cc: ralf@linux-mips.org
Cc: heiko@sntech.de
Cc: icenowy@aosc.io
Cc: ak@linux.intel.com
Cc: laurent.pinchart@ideasonboard.com
Cc: krzk@kernel.org
Cc: geert+renesas@glider.be
Cc: paul@crapouillou.net
Cc: prasannatsmkumar@gmail.com
Cc: keescook@chromium.org
Cc: ebiederm@xmission.com
Cc: sernia.zhou@foxmail.com
Cc: zhenwenjin@gmail.com
Cc: 772753199@qq.com