* Propogate non-default pico_cmake_set_default values through to compile definitions
Add PICO_BOARD_CMAKE_OVERRIDES common scope variable, to contain any pico_cmake_set_default
CMake variables which have been overwritten. This allows passing CMake arguments to the
build, without needing extra target_compile_definitions.
Also add pico_cmake_set_default PICO_RP2350_A2_SUPPORTED to enable/disable the E10 abs-block fix
* Fix more board files missing pico_cmake_set_default PICO_RP2350_A2_SUPPORTED
* Apply @lurch's patch to check_board_header.py
* Modify check_board_header.py to work with both RP2040- and RP2350-based boards
* Tweaks to the board-header files so that they pass check_board_header.py
* Update tools/check_board_header.py
so that it handles pico_cmake_set_default the same way as cmake/generic_board.cmake does
* 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
