ARM: 6455/2: Better use of the RTC framework for sa11xx.

This patch uses the RTC framework to treat some common ioctl.

In particular, it fixes the behaviour of rtc_irq_set_freq(), which did
not work as expected because the timer was not beeing retriggered.

Signed-off-by: Marcelo Roberto Jimenez <mroberto@cpti.cetuc.puc-rio.br>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>