RP2040: Add support for the RP2040.

[skilau]

P2040: Add support for the RP2040.

This patch is a small patch that adds in the required ifdefs to make the async web server work on the RP2040 platform.

It requires the use of the "AsyncTCP_RP2040W" package from here: https://github.com/khoih-prog/AsyncTCP_RP2040W

This pull request is being done in tandem with the main pull request on esphome here: https://github.com/esphome/esphome/pull/5305

[LorbusChris]

@jesserockz could you take a look at this?

[esphome[bot]]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks :+1:

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[mathieucarbou]

FYI, I am maintaining since a few months now a fork which is more up to date, compatible with Arduino 2 and 3, and which is already used in many big projects around.

https://github.com/mathieucarbou/ESPAsyncWebServer

And we also have a working PR under test for RP2040: https://github.com/mathieucarbou/ESPAsyncWebServer/pull/31