RTC: periodic irq fix

Add kernel/kernel and kernel/user locking for the periodic irq feature of
the rtc class.

PIE ioctls are also supported.

Signed-off-by: Alessandro Zummo <a.zummo@towertech.it>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>