Check if /dev/serial0 points to the correct device on all Pis

[golemparts]

By default, Uart::new uses /dev/serial0 to find the correct UART device to use. On the Raspberry Pi 5, this points to /dev/ttyAMA10 instead of /dev/ttyAMA0, which is the debug UART/console. We need to check if using this still makes sense on all Pi devices, or if we need to use a different default based on the Pi we're running on. Currently, calling with_path instead of new is a valid workaround.

Also update the documentation to reflect Pi 5-specific configuration options to configure UART.

Also see #165.

[Dygear]

Worth a mention that on the Raspberry Pi 5, I needed to put dtoverlay=uart0-pi5 into my /boot/firmware/config.txt file (at the bottom, can be placed in the [all] section, but [pi5] is also acceptable, but doesn't exist by default). That is what enabled me to use the GPIO 14/15 pins when reaching into /dev/ttyAMA0. The configuration here is a little tricky as it's not very well documented on the Raspberry Pi foundation side. Everything is there, but they don't outright call it out when you go to the UART section of the manual for the Raspberry Pi 5.