Although the rpi_pico can already build and run with the zephyr port, this
configuration improves it in a number of ways:
- Use the USB CDC ACM as the REPL, rather than just a UART.
- Enable I2C and SPI, and add I2C1.
- Enable a filesystem, which matches exactly the rp2 port's RPI_PICO
configuration. So switching between zephyr and rp2 is possible and will
retain the filesystem.
- Make the MicroPython GC heap make the most use of the available RAM.
Signed-off-by: Damien George <damien@micropython.org>