MIPS: Loongson64: Switch the order of RS780E and LS7A

Sort the members of enum in alphabetical order is better to avoid
duplicate mistakes (because the list may be grow very large), so
fix it by exchanging the order.

Signed-off-by: Liangliang Huang <huangll@lemote.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>