Add LAN8720 support for Raspberry Pico

**Describe the problem you have/What new integration you would like**
LAN8720 module doesn't work with Raspberry Pico - fails during validation: `Component ethernet requires component esp32.`

**Please describe your use case for this integration and alternatives you've tried:**
Alternative: Raspberry Pico-W with wifi, but it's a no-go in this situation (no Wifi at the place).

**Additional context**

Start by reviewing the ethernet component validation that currently reports “Component ethernet requires component esp32.” No source files or tests are named in the request. Done would mean LAN8720 support works on Raspberry Pico without the ESP32-only validation failure.

Written by the indexing model from the issue text.