drivers/rtc/rtc-s5m.c: add support for S2MPS13 RTC

The S2MPS13 RTC is almost the same as S2MPS14. The differences when
updating alarm are:
1. Set WUDR+AUDR field instead of WUDR+RUDR.
2. Clear the AUDR field later (it is not auto-cleared).

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>