tests: rtc: Adjust RTC samples tests for NXP RTC

This patch adjusts some of the timeouts for the RTC sample test.  The
NXP RTC varies a little bit from the QMSI due to the way the timer
count and alarm count work.  The NXP will trigger an alarm when the
timer count and alarm count are the same, but only when it increments
to the next value.

If you set the alarm to be 1 second past the current time, it may take
up to 2 seconds.  Setting the alarm equal to the current time will
result in an alarm occurring in less than 1 elapsed second.

Signed-off-by: Andy Gross <agross@kernel.org>