time: Add y2038 safe read_persistent_clock64()

As part of addressing in-kernel y2038 issues, this patch adds
read_persistent_clock64() and replaces all the call sites of
read_persistent_clock() with this function. This is a __weak
implementation, which simply calls the existing y2038 unsafe
read_persistent_clock().

This allows architecture specific implementations to be
converted independently, and eventually the y2038 unsafe
read_persistent_clock() can be removed after all its
architecture specific implementations have been converted to
read_persistent_clock64().

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1427945681-29972-3-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 18d27a3..4c0f76f4 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -268,6 +268,7 @@
 }
 
 extern void read_persistent_clock(struct timespec *ts);
+extern void read_persistent_clock64(struct timespec64 *ts);
 extern void read_boot_clock(struct timespec *ts);
 extern void read_boot_clock64(struct timespec64 *ts);
 extern int update_persistent_clock(struct timespec now);