rtc: rtc-sh: use set_irq_wake()

Modify the sh_rtc driver to use set_irq_wake() during suspend
and resume. These functions are used to enable the rtc interrupts
in the interrupt controller so the rtc can be used to wakeup the
system from suspend.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>