I am using GPIO(CON3) pins 8 and 10 for a project. In BPI M1+, functions for those pins are PH0 and PH1 respectively.
https://bananapi.gitbooks.io/bpi-m1-bpi-m1-plus-/content/en/bpi-m1+_gpio_pin_define.html
But, when I added overlays=uart3 ,I didn't work properly . When I checked the overlay file sun7i-a20-uart3.dtbo , by changing it to .dts , I figured out that this overlay file uses PG6,PG7 pins, not PH0,PH1 pins.
So, to modify the configurations without adding uart3 overlay in the /boot/armbianEnv.txt file, I wanted to edit the /boot/dtb/sun7i-a20-bananapi-m1-plus.dtb