time: Consolidate the time accessor prototypes

Right now we have time related prototypes in 3 different header
files. Move it to a single timekeeping header file and move the core
internal stuff into a core private header.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>
diff --git a/kernel/time/time.c b/kernel/time/time.c
index e8121a6..278c63c 100644
--- a/kernel/time/time.c
+++ b/kernel/time/time.c
@@ -42,6 +42,7 @@
 #include <asm/unistd.h>
 
 #include "timeconst.h"
+#include "timekeeping.h"
 
 /*
  * The timezone where the local system is located.  Used as a default by some