rtc: pcf8563: Clear event flags and disable interrupts before requesting irq

Besides the alarm, the PCF8563 also has a timer triggered interrupt.
In cases where the previous system left the timer and interrupts on,
or somehow the bits got enabled, the interrupt would keep triggering
as the kernel doesn't know about it.

Clear both the alarm and timer event flags, and disable the interrupts,
before requesting the interrupt line.

Fixes: ede3e9d4 ("drivers/rtc/rtc-pcf8563.c: add alarm support")
Fixes: a45d528a ("rtc: pcf8563: clear expired alarm at boot time")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>