rtc: cros-ec: Detect and report supported alarm window size

rtc: cros-ec: Detect and report supported alarm window size

The RTC on some older Chromebooks can only handle alarms less than
24 hours in the future. The only way to find out is to try to set
an alarm further in the future. If that fails, assume that the RTC
connected to the EC can only handle less than 24 hours of alarm
window, and report that value to the RTC core.

After that change, it is no longer necessary to limit the alarm time
when setting it. Report any excessive alarms to the caller instead.

Cc: Brian Norris <briannorris@chromium.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20230817225537.4053865-4-linux@roeck-us.net
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>