MIPS: Alchemy: add sysdev for IRQ PM.

Use a sysdev to implement PM methods for the Au1000 interrupt controllers.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
To: Linux-MIPS <linux-mips@linux-mips.org>
Patchwork: http://patchwork.linux-mips.org/patch/1114/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>