drivers/rtc/rtc-twl.c: ensure IRQ is wakeup enabled

Currently, the RTC IRQ is never wakeup-enabled so is not capable of
bringing the system out of suspend.

On OMAP platforms, we have gotten by without this because the TWL RTC is
on an I2C-connected chip which is capable of waking up the OMAP via the IO
ring when the OMAP is in low-power states.

However, if the OMAP suspends without hitting the low-power states (and
the IO ring is not enabled), RTC wakeups will not work because the IRQ is
not wakeup enabled.

To fix, ensure the RTC IRQ is wakeup enabled whenever the RTC alarm is
set.

Signed-off-by: Kevin Hilman <khilman@linaro.org>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>