rtc: cmos: Report supported alarm limit to rtc infrastructure

The alarm window supported by the cmos RTC depends on the chip
and its configuration. Report the limit to the RTC core.

Cc: Brian Norris <briannorris@chromium.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20230817225537.4053865-5-linux@roeck-us.net


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