x86: build fix for "x86: fix C1E && nx6325 stability problem"

fix:

arch/x86/kernel/acpi/boot.c: In function ‘dmi_ignore_irq0_timer_override’:
arch/x86/kernel/acpi/boot.c:1443: error: implicit declaration of function ‘force_mask_ioapic_irq_2’

Signed-off-by: Ingo Molnar <mingo@elte.hu>