Despite the [silk on the dock board](https://wiki.makerdiary.com/nrf52840-m2-devkit/resources/nrf52840_m2_devkit_hw_diagram_v1_0.pdf), the SDA/SCL pins weren't defined. Though, they were already defined in `mpconfigboard.h`.
Same for RX/TX. It looks like it declared `TXD` and `RXD`, so I didn't want to remove those, but I think it makes sense to have the "standard" pin names, but I moved ithem to illustrate they were all referencing the same pins.
I mimicked the whitespace I saw in the metro_nrf52840_express port.
Mark Roberts
nitz
Yihui Xiong