MIPS: Loongson64: DeviceTree for LS7A PCH

Add DeviceTree files for Classic Loongson64 Quad Core + LS7A boards and
Generic Loongson64 Quad Core + LS7A boards.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Tested-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>