[Internal pull-up on UART rx?]

[H5: Nanopi neo core 2]

I observe the UART Rx line to be influenced by the RTS line which I am using during sending. Is there a way to enable an internal pull-up on Rx so that this doesn't happen? I suspect it's the cause of communication errors that I observe. I confess that I am currently on a FriendlyCore 4.16 build, but I wouldn't expect such an issue to be too distribution-specific.

[dtc does not support compiling overlays]

Getting a more recent version of dtc (1.4.7 instead of 1.4.0 which comes by default) solves the issue, but it'd be nice if this worked out of the box.

[dtc does not support compiling overlays]

I built Armbian_5.59_Nanopineocore2_Ubuntu_xenial_next_4.17.17.img for my board, and am trying to add an overlay dtb that describes a port expander I have on i2c2. 

$ sudo armbian-add-overlay ./mcp23008.dts 
Error: dtc does not support compiling overlays
Please try to install matching kernel headers