[PATCH] powerpc32: fix definition of distribute_irqs

When we select ppc32 under the powerpc architecture we get the
error below.  This relates to defining distribute_irqs when this
configuratiom option is undefined.

      CC      arch/powerpc/sysdev/mpic.o
    .../arch/powerpc/sysdev/mpic.c: In function `mpic_setup_this_cpu':
    .../arch/powerpc/sysdev/mpic.c:788: error: `CONFIG_IRQ_ALL_CPUS'
	undeclared (first use in this function)

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>