Platform abstraction, CRPA LED heartbeat & MSPI support

The proposed changes include the following:

Aesthetics and comment typo fix
- Non-functional whitespace removal performed to minimize deltas in functional changesets
A simple platform abstraction introduced to decouple I/O and peripheral differences between platforms and builds.
- This has been introduced to allow for CRPA builds that target either "normal" use (with an added heartbeat LED) or the SPI master mode -- both cannot be used simultaneously due to pin multiplexing constraints.
- make CRPA=y or make CRPA_MSPI=y is now required to target the Crazyradio PA (and use the RXEN for the LNA.
- make builds a "generic" firmware that leaves P0 as inputs.
SPI Master support for modified CRPA platforms
- Utilities to dump and program nRF24LU1+ devices coming in future PRs

BastilleResearch / mousejack