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/arch/mips/lasat/sysctl.c b/arch/mips/lasat/sysctl.c
index 3b7f65c..cf9b4633 100644
--- a/arch/mips/lasat/sysctl.c
+++ b/arch/mips/lasat/sysctl.c
@@ -75,11 +75,11 @@
 int proc_dolasatrtc(struct ctl_table *table, int write,
 		       void *buffer, size_t *lenp, loff_t *ppos)
 {
-	struct timespec ts;
+	struct timespec64 ts;
 	int r;
 
 	if (!write) {
-		read_persistent_clock(&ts);
+		read_persistent_clock64(&ts);
 		rtctmp = ts.tv_sec;
 		/* check for time < 0 and set to 0 */
 		if (rtctmp < 0)