x86/ioapic.c: unify ioapic_retrigger_irq()

The 32 and 64-bit versions of ioapic_retrigger_irq() are identical
except the 64-bit one takes vector_lock.  vector_lock is defined and
used on 32-bit too, so just use a common ioapic_retrigger_irq().
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

arch/x86/kernel/apic/io_apic.c

@@ -2178,7 +2178,6 @@ static unsigned int startup_ioapic_irq(unsigned int irq)
 	return was_pending;
 }
 
-#ifdef CONFIG_X86_64
 static int ioapic_retrigger_irq(unsigned int irq)
 {
 
@@ -2191,14 +2190,6 @@ static int ioapic_retrigger_irq(unsigned int irq)
 
 	return 1;
 }
-#else
-static int ioapic_retrigger_irq(unsigned int irq)
-{
-	apic->send_IPI_self(irq_cfg(irq)->vector);
-
-	return 1;
-}
-#endif
 
 /*
  * Level and edge triggered IO-APIC interrupts need different handling,