Tested 14/09/2020 with FW 2.60 and Expander Pi

1 If not existing copy files ds1307-rtc-overlay.dtb and i2c-rtc-overlay.dtb to folder /u-boot/overlays. -> OK done.
2 Modify /u-boot/config.txt
	add to section [all]: dtoverlay=mcp3208:spi0-0-present,i2c-rtc,ds1307-rtc
	add: dtparam=i2c_arm=on
3 Modify/create /etc/rc.local
	add: echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-1/new_device
	add: hwclock -s
4 make rc.local executable by following command: chmod 755 /etc/rc.local
5 reboot
4 modprobe i2c-dev
5 i2cdetect -y 1 -> confirms RTC hardware is recognized and kernel driver is loaded when "UU" is shown in table
6 hwclock -r -> Results in something like: Sat 1 Jan 00:00:31 2000 0.000000 seconds
7 date -> when connected to internet and synchronized to NTP server shows actual date/time
8 hwclock -w -> writes actual date/time to RTC
9 hwclock -r -> verify that RTC time is now okay
10 Finished!