The interfaces based on 'struct timespec' and 'unsigned long' seconds
are no longer recommended for new code, and we are trying to migrate to
ktime_t based interfaces and other y2038-safe variants.

This moves all the legacy interfaces from linux/timekeeping.h into a
new timekeeping32.h to better document this.

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>