MIPS: Loongson64: Reorder CPUCFG model match arms

Originally the match arms are ordered by model release date, however
the LOONGSON_64R cores are even more reduced capability-wise. So put
them at top of the switch block.

Suggested-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>