MIPS: Loongson: pm: Remove redundant source code

The implmentation of loongson2e_power_off and loongson2e_halt is almostly
the same, just preserve one of them.

Signed-off-by: Wu Zhangjin <wuzj@lemote.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>