irqchip: move mmp irq driver

Move irq-mmp driver from mach-mmp directory into irqchip directory.
It's used to support multiple platform.

Signed-off-by: Haojian Zhuang <haojian.zhuang@gmail.com>

arch/arm/mach-mmp/common.h

@@ -3,7 +3,6 @@
 
 extern void timer_init(int irq);
 
-extern void __init icu_init_irq(void);
 extern void __init mmp_map_io(void);
 extern void mmp_restart(enum reboot_mode, const char *);
 extern void __init pxa168_clk_init(void);