[POWERPC] Add missed include

fixes:
arch/powerpc/platforms/pasemi/idle.c: In function 'pasemi_system_reset_exception':
arch/powerpc/platforms/pasemi/idle.c:55: warning: implicit declaration of function 'do_IRQ'

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>