MIPS: Loongson 2F: Add suspend support framework

This patch add basic suspend support for loongson2f family machines,
loongson2f have a specific feature: when we set it's frequency to ZERO,
it will go into a wait mode, and then can be waked up by the external
interrupt. so, if we setup suitable interrupts before putting it into
wait mode, we will be able wake it up whenever we want via sending the
relative interrupts to it.

These interrupts are board-specific, Yeeloong2F use the keyboard
interrupt and SCI interrupt, but LingLoong and Fuloong2F use the
interrupts connected to the processors directly. and BTW: some old
LingLoong and FuLoong2F have no such interrupts connected, so, there is
no way to wake them up from suspend mode. and therefore, please do not
enable the kernel support for them.

The board-specific support will be added in the coming patches.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: yanh@lemote.com
Cc: huhb@lemote.com
Cc: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: linux-pm@lists.linux-foundation.org
Patchwork: http://patchwork.linux-mips.org/patch/629/


Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>