drivers/rtc/rtc-tps65910.c: enable/disable wake in suspend/resume

Making the rtc driver as wakeup capabale and leaving the wake
enable/disable decision to user space through a sysfs attribute.

In suspend, enable wake if device wakeup enabled.  In resume disable wake
again.

This change is inline with the Documentation/power/devices.txt#
/sys/devices/.../power/wakeup files

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>