MIPS: Ingenic: Add CPU nodes for Ingenic SoCs.

Add 'cpus' node to the jz4725b.dtsi, jz4740.dtsi, jz4770.dtsi,
jz4780.dtsi, x1000.dtsi, and x1830.dtsi files.

Tested-by: H. Nikolaus Schaller <hns@goldelico.com>
Tested-by: Paul Boddie <paul@boddie.org.uk>
Signed-off-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@wanyeetech.com>
Reviewed-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>