rtc-vr41xx: add irq_set_freq() and irq_set_state()

Implement the ioctls RTC_PIE_ON, RTC_PIE_OFF, RTC_IRQP_SET and
RTC_IRQP_READ in the standard RTC way.

Thanks Dave for noticing it.

Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Cc: David Brownell <david-b@pacbell.net>
Cc: Ralf Baechle <ralf@linux-mips.org>
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>