irq: sparse irqs, fix #3

fix non-APIC UP build:

 arch/x86/kernel/built-in.o: In function `setup_arch':
 : undefined reference to `pin_map_size'
 arch/x86/kernel/built-in.o: In function `setup_arch':
 : undefined reference to `first_free_entry'

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