This fixes some missing and incorrectly-assigned pins for the SparkFun Thing Plus RP2040 protoboard so that they actually match what the board says. This also changes the default SPI pins from the SD card pins to the breakout pins on the side of the board.
This switches stage2 to C and uses Jinja to change the C code based
on flash settings from https://github.com/adafruit/nvm.toml. It
produces the fastest settings for the given set of external flashes.
Flash size is no longer hard coded so switching flashes with similar
capabilities but different sizes should *just work*.
This PR also places "ITCM" code in RAM to save the XIP cache for
code execution. Further optimization is possible. A blink code.py
still requires a number of flash fetches every blink.
Fixes#4041
