drivers/rtc/rtc-ds3232.c: enable ds3232 to work as wakeup source

Add suspend/resume and device_init_wakeup to enable ds3232 as wakeup
source, /sys/class/rtc/rtcX/wakealarm for set wakeup alarm.

Signed-off-by: Wang Dongsheng <dongsheng.wang@freescale.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>