x86, ioapic: Add dummy ioapic functions

Some ioapic extern functions are used when CONFIG_X86_IO_APIC is not
defined.  We need the dummy functions to avoid a compile time error.
Signed-off-by: NJacob Pan <jacob.jun.pan@intel.com>
LKML-Reference: <43F901BD926A4E43B106BF17856F0755A318DA07@orsmsx508.amr.corp.intel.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

arch/x86/include/asm/io_apic.h

@@ -197,7 +197,11 @@ static const int timer_through_8259 = 0;
 static inline void ioapic_init_mappings(void)	{ }
 static inline void ioapic_insert_resources(void) { }
 static inline void probe_nr_irqs_gsi(void)	{ }
+static inline int mp_find_ioapic(int gsi) { return 0; }
 
+struct io_apic_irq_attr;
+static inline int io_apic_set_pci_routing(struct device *dev, int irq,
+		 struct io_apic_irq_attr *irq_attr) { return 0; }
 #endif
 
 #endif /* _ASM_X86_IO_APIC_H */