Support LibreTiny platform

[kuba2k2]

This PR adds support for the LibreTiny platform, supported in ESPHome for a few months now.

This has been tested on BK7231T chip (should also work on BK7231N), it works flawlessly after a tiny change in LibreTiny.

The Realtek RTL8710B platform wasn't tested.

No ESPHome changes are required for this to work (well, a LibreTiny version bump is).

[kuba2k2]

The reason for the draft status was that I had to check something - I had issues with TCP (ping worked fine), it turned out to be caused by lack of netmask: setting in my ESPHome YAML.

[droscy]

Hello @kuba2k2, thanks for your contribution.
I don't own a LibreTiny board, so the only test I can perform is compiling the firmware.

What do you mean with "a LibreTiny version bump is"? Do I need to wait for some ESPHome PR to be merged in dev to compile this code or is it working with the current dev?

[kuba2k2]

Hi,
the code needs the latest (not released, yet) version of LibreTiny to work properly - a certain mbedTLS setting prevents it from connecting to WireGuard without that fix.

So yes, an ESPHome PR will be required in order to make the new version available by default - otherwise, one can just use version: 1.5.x. to force a specific LibreTiny version.

A PR for ESPHome should include esp_wireguard version bump, as well. So, this library should be updated before the ESPHome PR is made. You don't need to wait for ESPHome PR, also this change is non-breaking so ESP8266/ESP32 users will not notice any changes.