x86, UV: add uv_setup_irq() and uv_teardown_irq() functions, v3, fix

fix:

 arch/x86/kernel/uv_irq.c: In function 'uv_ack_apic':
 arch/x86/kernel/uv_irq.c:26: error: implicit declaration of function 'ack_APIC_irq'

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