rtc: update vr41xx alarm handling

- vr41xx_rtc_read_alarm() reports alarm enabled.
- vr41xx_rtc_set_alarm() sets alarm disable/enable by rtc_wkalrm.enabled.

Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>