Add function to wait for RTC shadow register initialization
Add function to wait for RTC shadow register initialization

The function periodically checks whether the RSF flag in the RTC->ISR
register has been set. For this to work correctly, the flag needs to
be cleared when waking up from Stop or Standby modes. This is taken
care of by an earlier patch in this series.

bigclownlabs/bc-core-module-sdk,bigclownlabs/bc-core-module-sdk,bigclownlabs/bc-core-module-sdk