i386, apic: fix 4 bit apicid assumption of mach-default

Andi/Andrew,

Can you pick this up for your trees and if there are no issues, can you please push it to mainline before .23 gets released.

We have seen a boot failure with fewer cpu sockets populated on a MP platform. Similar problem can happen on a fully populated system, if # of cpus <= 8 and any of the apic id's is > 16

thanks,
suresh
---
Fix get_apic_id() in mach-default, so that it uses 8 bits incase of xAPIC case and 4 bits for legacy APIC case.

This fixes the i386 kernel assumption that apic id is less than 16 for xAPIC platforms with 8 cpus or less and makes the kernel boot on such platforms.

---

index 7bcb350..ae98413 100644
@@ -1,11 +1,17 @@
 #ifndef __ASM_MACH_APICDEF_H
 #define __ASM_MACH_APICDEF_H
 
+#include <asm/apic.h>
+
 #define		APIC_ID_MASK		(0xF<<24)
 
 static inline unsigned get_apic_id(unsigned long x) 
 { 
-	return (((x)>>24)&0xF);
+	unsigned int ver = GET_APIC_VERSION(apic_read(APIC_LVR));
+	if (APIC_XAPIC(ver))
+		return (((x)>>24)&0xFF);
+	else
+		return (((x)>>24)&0xF);
 } 
 
 #define		GET_APIC_ID(x)	get_apic_id(x)