rtc: da9063: Make IRQ as optional

On some platforms (eg: RZ/{G2UL,Five} SMARC EVK), there is no IRQ
populated by default. Add irq optional support.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20240105145344.204453-2-biju.das.jz@bp.renesas.com


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