This commit enables optional reset of the RTC, in case
its registers' contents did not sustain the reboot or power-off/on
sequence. Without it, further usage of RTC is impossible (e.g.
writing values to RTC_TIME register will not succeed).
The reset is performed only if Clock Correction register
does not comprise RTC_NOMINAL_TIMING, what helps to
distinguish, whether the software configured RTC before or it comprises
the default value.