There're many sites need comparing the two rtc_time variants for many
rtc drivers, especially in the instances of rtc_class_ops::set_alarm().
So add this common helper function to make things easy.
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>