time: Move time_t conversion helpers to time32.h

On 64-bit architectures, the timespec64 based helpers in linux/time.h
are defined as macros pointing to their timespec based counterparts.
This made sense when they were first introduced, but as we are migrating
away from timespec in general, it's much less intuitive now.

This changes the macros to work in the exact opposite way: we always
provide the timespec64 based helpers and define the old interfaces as
macros for them. Now we can move those macros into linux/time32.h, which
already contains the respective helpers for 32-bit architectures.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Miroslav Lichvar <mlichvar@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Stephen Boyd <stephen.boyd@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>

kernel/time/time.c

@@ -407,6 +407,7 @@ time64_t mktime64(const unsigned int year0, const unsigned int mon0,
 }
 EXPORT_SYMBOL(mktime64);
 
+#if __BITS_PER_LONG == 32
 /**
  * set_normalized_timespec - set timespec sec and nsec parts and normalize
  *
@@ -467,6 +468,7 @@ struct timespec ns_to_timespec(const s64 nsec)
 	return ts;
 }
 EXPORT_SYMBOL(ns_to_timespec);
+#endif
 
 /**
  * ns_to_timeval - Convert nanoseconds to timeval
@@ -486,7 +488,6 @@ struct timeval ns_to_timeval(const s64 nsec)
 }
 EXPORT_SYMBOL(ns_to_timeval);
 
-#if BITS_PER_LONG == 32
 /**
  * set_normalized_timespec - set timespec sec and nsec parts and normalize
  *
@@ -547,7 +548,7 @@ struct timespec64 ns_to_timespec64(const s64 nsec)
 	return ts;
 }
 EXPORT_SYMBOL(ns_to_timespec64);
-#endif
+
 /**
  * msecs_to_jiffies: - convert milliseconds to jiffies
  * @m:	time in milliseconds