x86: map vsyscalls early enough

map vsyscalls early enough. This is important if a __vsyscall_fn
function is used by other kernel code too.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

include/asm-x86/vsyscall.h

@@ -36,6 +36,8 @@ extern volatile unsigned long __jiffies;
 extern int vgetcpu_mode;
 extern struct timezone sys_tz;
 
+extern void map_vsyscall(void);
+
 #endif /* __KERNEL__ */
 
 #endif /* _ASM_X86_64_VSYSCALL_H_ */