x86/acpi: store ACPI ids from MADT for future usage

Currently we don't save ACPI ids (unlike LAPIC ids which go to
x86_cpu_to_apicid) from MADT and we may need this information later.
Particularly, ACPI ids is the only existent way for a PVHVM Xen guest
to figure out Xen's idea of its vCPUs ids before these CPUs boot and
in some cases these ids diverge from Linux's cpu ids.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index 678637a..a7fb9dd 100644
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -16,6 +16,7 @@
 static inline void prefill_possible_map(void) {}
 
 #define cpu_physical_id(cpu)			boot_cpu_physical_apicid
+#define cpu_acpi_id(cpu)			0
 #define safe_smp_processor_id()			0
 #define stack_smp_processor_id()		0