J721e/j7200: MCU/WKUP UART as console. The output gets garbled after sysfw/dm load

flash all images using MCU_UART in UART boot mode. Adapt ATF, TISPL and u-boot so that MCU_UART is used instead of Main_UART (so all binaries can be flashed using same console/UART).

After loading Sysfw; seems baud rate is changing to 230400, so we need to flash TISPL with 230400 baud rate instead of 115200. Again we need to set baudrate back to 115200 to flash uboot-img.