selftest: rtc: skip some tests if the alarm only supports minutes

There are alarms which have only minute-granularity. The RTC core
already has a flag to describe them. Use this flag to skip tests which
require the alarm to support seconds.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20250218101548.6514-1-wsa+renesas@sang-engineering.com


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