rtc: sh: simplify irq setup after refactoring

We only need the alarm_irq handler. That means we can remove everything
related to periodic_irq and carry_irq. Also, the shared handler can go
since we only we need the alarm interrupt in any case.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20250227134256.9167-15-wsa+renesas@sang-engineering.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>