FIFO status register.
| RXFIFO_RADDR | Represents the offset address of the APB reading from RXFIFO |
| RXFIFO_WADDR | Represents the offset address of i2c module receiving data and writing to RXFIFO. |
| TXFIFO_RADDR | Represents the offset address of i2c module reading from TXFIFO. |
| TXFIFO_WADDR | Represents the offset address of APB bus writing to TXFIFO. |