* Small whitespace fixup
* typo bugfix
* Small refactoring of check_board_header.py
* Make structure of rp2040_interface_pins.json more explicit, so that it can be more easily extended
* Move definition of valid-pins from python to json
* Check that each interface includes all (minimally) expected pins
Note that UART_CTS, UART_RTS & SPI_CSN are classed as optional
* Split "expected_functions" into "required" (all of these pins must be present) and "one_of" (at least one of these pins must be present)
* Add script to automatically validate board header files
* Fix small automatically-found inconsistencies in various board header files
* Tweak and add board header file from abandoned PR #1174
