xen: expose enable_IO_APIC for 32-bit

enable_IO_APIC() is defined for both 32- and 64-bit x86, so it should
be declared for both.
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

arch/x86/include/asm/hw_irq.h

@@ -65,9 +65,7 @@ extern void disable_IO_APIC(void);
 extern int IO_APIC_get_PCI_irq_vector(int bus, int slot, int fn);
 extern void setup_ioapic_dest(void);
 
-#ifdef CONFIG_X86_64
 extern void enable_IO_APIC(void);
-#endif
 
 /* Statistics */
 extern atomic_t irq_err_count;