Pin defines are:
- For Pico define board pins and the default LED pin (WL_GPIO25).
- For Pico-W define board pins, external pins and the default
LED pin (WL_GPIO0).
- For the Nano-RP2040, define board pins, external pins and
the default LED pin (GPIO25)
- For all other boards, the pins.csv defines the LED pin (if any)
for backwards compatibility with code that assumes there's always
an LED pin.
Handle externally controlled GPIO pins more generically, by removing all
CYW43-specific code from `machine_pin.c`, and adding hooks to initialise,
configure, read and write external pins. This allows any driver for an
on-board module which controls GPIO pins (such as CYW43 or NINA), to
provide its own implementation of those hooks and work seamlessly with
`machine_pin.c`.
