x86, acpi/irq: Define gsi_end when X86_IO_APIC is undefined

My recent changes introducing a global gsi_end variable
failed to take into account the case of using acpi on a system
not built to support IO_APICs, causing the build to fail.

Define gsi_end to 15 when CONFIG_X86_IO_APIC is not set to avoid
compile errors.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <m1tyqm14la.fsf_-_@fess.ebiederm.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/io_apic.h

@@ -197,6 +197,7 @@ 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)	{ }
+#define gsi_end (NR_IRQS_LEGACY - 1)
 static inline int mp_find_ioapic(u32 gsi) { return 0; }
 
 struct io_apic_irq_attr;