x86/timers: Move the simple udelay calibration to tsc.h

Commit dd759d93f4dd ("x86/timers: Add simple udelay calibration") adds
an static function in x86 boot-time initializations.

But, this function is actually related to TSC, so it should be maintained
in tsc.c, not in setup.c.

Move simple_udelay_calibration() from setup.c to tsc.c and rename it to
tsc_early_delay_calibrate for more readability.

Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/1500003247-17368-1-git-send-email-douly.fnst@cn.fujitsu.com

diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index f5e6f1c..d0509c7 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -31,6 +31,7 @@ static inline cycles_t get_cycles(void)
 
 extern struct system_counterval_t convert_art_to_tsc(u64 art);
 
+extern void tsc_early_delay_calibrate(void);
 extern void tsc_init(void);
 extern void mark_tsc_unstable(char *reason);
 extern int unsynchronized_tsc(void);