W5500 support for RP2040

**Describe the problem you have/What new integration you would like**

Support for W5500 ethernet on the RP2040 platform

**Please describe your use case for this integration and alternatives you've tried:**

The combination of the PoE FeatherWing and the RP2040-shim from Silicognition makes for an extremely compact wired sensor. Sometimes you need to put a sensor where WiFi doesn't travel well (underground in my specific case), and running a single ethernet cable with PoE is more convenient than having to also supply power separately. Currently the only way to use this platform with Home Assistant is with MQTT.

**Additional context**

W5500 support was added for the ESP32 platform in https://github.com/esphome/esphome/pull/4424, but not for RP2040.

Start by reviewing the W5500 ESP32 implementation linked in PR #4424 and compare its requirements with the RP2040 platform. Define the integration points and validation needed for W5500 Ethernet on RP2040; done means the platform can use the hardware for the stated wired sensor use case.

Written by the indexing model from the issue text.