Read measured position from the DWM1001C

[tmplt]

Measured position data can be extracted in two a few ways:

• UART over USB: After establishing a connection via minicom -D /dev/ttyACM0 -b 115200, pressing enter twice we get a CLI. Entering lep prints the measured position each tick IF we are communicating with at least three anchors. The command les behaves similarly, but also prints which (and thus how many) anchors the data was derived from. lep prints data on the form POS,X,Y,Z,Q, where Q is a quality factor.
• Bluetooth: As used in the Decawave DRTLS Manager.
• GPIO pinout: The development board is reportedly compatible with Raspberry Pis. Data can likely be extracted over I2C or UART.

Of the above, data via the board's GPIO is the preferred method as communication will likely be similar to that of the BrickPi3; We should be able to just stack the components upon the Pi, and drive them all via the barrel connector of the BrickPi. If this approach fails/takes too long to implement, we can readily read the data over USB.

While the Raspberry Pi has Bluetooth capabilities, reading the data with that approach is a bad idea: position data will be greatly outdated when we receive it, and the delay is not predictable.

[tmplt]

Data can (and have been reported by others) be read via the UART pins on the RPi with the same baud rate as over USB UART. However, the hardware does not play ball with NixOS: while the expected /dev/ttyAMA0 is available when booting with boot.kernelPackages = pkgs.linuxPackages_rpi3, a simple loopback test (bridge UART RX and TX pins) does not pass. For now we'll read data over the USB UART interface: /dev/ttyACM0.

[tmplt]

• Tested with enable_uart=1 in /boot/config.txt without any effect. Do we have to specify force_turbo=1 also?
• Does it work with some UART overlay from https://github.com/raspberrypi/linux/tree/rpi-4.19.y/arch/arm/boot/dts/overlays using https://github.com/NixOS/nixpkgs/pull/99378?
• boot.kernelParams lib.mkForce []; was set. Does that cause issues?