rtc: stm32: add alarm A out feature

rtc: stm32: add alarm A out feature

STM32 RTC can pulse some SOC pins when an RTC alarm expires.
This patch adds this functionality for alarm A. The pulse can out on three
pins RTC_OUT1, RTC_OUT2, RTC_OUT2_RMP (PC13, PB2, PI8 on stm32mp15)
(PC13, PB2, PI1 on stm32mp13) (PC13, PF4/PF6, PI8 on stm32mp25).

This patch only adds the functionality for devices which are using
st,stm32mp1-rtc and st,stm32mp25-rtc compatible.

Add "alarm-a" in pinmux functions.

Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240722160022.454226-5-valentin.caron@foss.st.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>