x86/rtc: Stop using deprecated functions

rtc_time_to_tm() and rtc_tm_to_time() are deprecated because they
rely on 32bits variables and that will make rtc break in y2038/2016.

Use the proper y2038 safe functions.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Stephen Boyd <stephen.boyd@linaro.org>
Cc: Miroslav Lichvar <mlichvar@redhat.com>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Link: https://lkml.kernel.org/r/1520620971-9567-5-git-send-email-john.stultz@linaro.org