RTC fast memory configuration register
| RTC_MEM_CRC_START | Set this bit to start the CRC of RTC memory. | 
| RTC_MEM_CRC_ADDR | This field is used to set address of RTC memory for CRC. | 
| RTC_MEM_CRC_LEN | This field is used to set length of RTC memory for CRC based on start address. | 
| RTC_MEM_CRC_FINISH | This bit stores the status of RTC memory CRC. High level means finished while low level means not finished. |