Add support for various SPI-based ethernet chips (W5500, KSZ8851SNL,
DM9051) to the ESP32 port. This leverages the existing support in ESP-IDF
for these chips -- which configures these chips in "MAC raw" mode -- and
the existing support for network.LAN in the ESP32 port. In particular,
this doesn't leverage the wiznet5k support that is used on the rp2 and
stm32 ports (because that's for native use of lwIP).
Tested on the POE Featherwing (with the SJIRQ solder jumper bridged) and a
ESP32-S3 feather.
A note about the interrupt pin: The W5500 implementation within ESP-IDF
relies on hardware interrupt, and requires the interrupt pin from the W5500
to be wired to a GPIO. This is not the case by default on the Adafruit
Ethernet FeatherWing, which makes it not directly compatible with this
implementation.
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