Thanks for the responses!
Unfortunately, I already soldered in a DS3231 board, as it was the only board that would fit in the Zebra case I used (I had to remove the serial connector for even that board to fit)
Could I replace
fdtput -t s /flash/dtb.img /i2c@c1108500/pcf8563@51 status "okay"
echo "rtc_pcf8563" >> /storage/.config/modprobe.d/rtc.conf
With
fdtput -t s /flash/dtb.img /i2c@c1108500/ds3231@51 status "okay"
echo "rtc_ds3231" >> /storage/.config/modprobe.d/rtc.conf
?
Also, in my searching I found evidence the DS3231 uses the DS1307 driver. Could I instead:
fdtput -t s /flash/dtb.img /i2c@c1108500/ds1307@51 status "okay"
echo "rtc_ds1307" >> /storage/.config/modprobe.d/rtc.conf