[acpi] Make a dummy mp_congig_ioapic_for_sci() function.

include/asm-i386/mpspec.h

@@ -37,8 +37,14 @@ extern void mp_register_lapic_address (u64 address);
 extern void mp_register_ioapic (u8 id, u32 address, u32 irq_base);
 extern void mp_override_legacy_irq (u8 bus_irq, u8 polarity, u8 trigger, u32 global_irq);
 extern void mp_config_acpi_legacy_irqs (void);
-extern void mp_config_ioapic_for_sci(int irq);
 extern void mp_parse_prt (void);
+
+#ifdef CONFIG_X86_IO_APIC
+extern void mp_config_ioapic_for_sci(int irq);
+#else
+static inline void mp_config_ioapic_for_sci(int irq)
+{ }
+#endif
 #endif /*CONFIG_ACPI_BOOT*/
 
 #define PHYSID_ARRAY_SIZE	BITS_TO_LONGS(MAX_APICS)