Add support for the Particle Ethernet FeatherWing

[suda]

This PR adds support for Particle Ethernet FeatherWing based on WIZnet W5500 chip for Particle Argon/Boron/Xenon.

Usage:

import board
import busio
import wiznet

spi = busio.SPI(clock=board.SCK, MOSI=board.MOSI, MISO=board.MISO)
eth = wiznet.WIZNET5K(spi, board.D5, board.D3)
# For some reason DHCP doesn't seem to work in my case
eth.ifconfig(('192.168.1.2', '255.255.255.0', '192.168.1.1', '1.1.1.1'))

[tannewt]

Thanks! This looks great. Note that we will likely move the Wiznet support out of the core and into a Python library with CircuitPython 6. That will make it easier to maintain and improve.