dt-bindings: MIPS: Add X2000E based CU2000-Neo.

Add bindings for Ingenic X2000E based board, prepare for later dts.

Signed-off-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@wanyeetech.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>