Devices with RTC backup-batteries have been shown (very rarely) to have
incorrect RTC prescaler values. Such incorrect values mean the RTC counts
fast or slow, and will be wrong forever if the power/backup-battery is
always present.
This commit detects such a state at start up (hard reset) and corrects it
by reconfiguring the RTC prescaler values.
Signed-off-by: Damien George <damien@micropython.org>
