x86/apic: Make x2apic_mode depend on CONFIG_X86_X2APIC

No point in having a static variable around which is always 0. Let the
compiler optimize code out if disabled.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Tony Luck <tony.luck@intel.com>
Link: http://lkml.kernel.org/r/20150115211702.363274310@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/include/asm/apic.h

@@ -106,8 +106,6 @@ extern u32 native_safe_apic_wait_icr_idle(void);
 extern void native_apic_icr_write(u32 low, u32 id);
 extern u64 native_apic_icr_read(void);
 
-extern int x2apic_mode;
-
 static inline bool apic_is_x2apic_enabled(void)
 {
 	u64 msr;
@@ -178,6 +176,7 @@ static inline u64 native_x2apic_icr_read(void)
 	return val;
 }
 
+extern int x2apic_mode;
 extern int x2apic_phys;
 extern int x2apic_preenabled;
 extern void check_x2apic(void);
@@ -210,8 +209,9 @@ static inline void x2apic_force_phys(void)
 {
 }
 
-#define	x2apic_preenabled 0
-#define	x2apic_supported()	0
+#define x2apic_mode		(0)
+#define	x2apic_preenabled	(0)
+#define	x2apic_supported()	(0)
 #endif
 
 extern void enable_IR_x2apic(void);

arch/x86/kernel/apic/apic.c

@@ -161,8 +161,8 @@ static __init int setup_apicpmtimer(char *s)
 __setup("apicpmtimer", setup_apicpmtimer);
 #endif
 
-int x2apic_mode;
 #ifdef CONFIG_X86_X2APIC
+int x2apic_mode;
 /* x2apic enabled before OS handover */
 int x2apic_preenabled;
 static int x2apic_disabled;