rtc: s35390a: set uie_unsupported

Alarms are only supported on a per minute basis. This is why
uie_unsupported is set. Furthermore issue a warning when a second based
alarm is requested.

Signed-off-by: Richard Leitner <richard.leitner@skidata.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>