MIPS: Loongson: Cleanup CONFIG_LOONGSON_SUSPEND.

MIPS: Loongson: Cleanup CONFIG_LOONGSON_SUSPEND.

Now LOONGSON_CHIPCFG register definition doesn't depend on CPUFREQ any
more, so CPU_SUPPORTS_CPUFREQ is no longer needed for suspend/resume.
Remove CONFIG_LOONGSON_SUSPEND and use CONFIG_SUSPEND instead.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Cc: John Crispin <john@phrozen.org>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11274/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>