Need 'irq_affinity' array when CONFIG_PROC_FS=n.

With CONFIG_PROC_FS=n, the irq_affinity[NR_IRQS] array
is not available in arch/i386/kernel code:

arch/i386/kernel/built-in.o(.text+0x10037): In function `do_irq_balance':
: undefined reference to `irq_affinity'
arch/i386/kernel/built-in.o(.text+0x101a9): In function `do_irq_balance':
: undefined reference to `irq_affinity'
Signed-off-by: Randy Dunlap <rddunlap@osdl.org>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>