cyw43: move crate to subdir.

cyw43/README.md

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+# cyw43
+
+WIP driver for the CYW43439 wifi chip, used in the Raspberry Pi Pico W. Implementation based on [Infineon/wifi-host-driver](https://github.com/Infineon/wifi-host-driver).
+
+## Current status
+
+Working:
+
+- Station mode (joining an AP).
+- AP mode (creating an AP)
+- Scanning
+- Sending and receiving Ethernet frames.
+- Using the default MAC address.
+- [`embassy-net`](https://embassy.dev) integration.
+- RP2040 PIO driver for the nonstandard half-duplex SPI used in the Pico W.
+- Using IRQ for device events
+- GPIO support (for LED on the Pico W)
+
+TODO:
+
+- Setting a custom MAC address.
+- Bus sleep (unclear what the benefit is. Is it needed for IRQs? or is it just power consumption optimization?)
+
+## Running the examples
+
+- `cargo install probe-rs-cli`
+- `cd examples/rpi-pico-w`
+### Example 1: Scan the wifi stations
+- `cargo run --release --bin wifi_scan`
+### Example 2: Create an access point (IP and credentials in the code)
+- `cargo run --release --bin tcp_server_ap`
+### Example 3: Connect to an existing network and create a server
+- `WIFI_NETWORK=MyWifiNetwork WIFI_PASSWORD=MyWifiPassword cargo run --release`
+
+After a few seconds, you should see that DHCP picks up an IP address like this
+```
+11.944489 DEBUG Acquired IP configuration:
+11.944517 DEBUG    IP address:      192.168.0.250/24
+11.944620 DEBUG    Default gateway: 192.168.0.33
+11.944722 DEBUG    DNS server 0:    192.168.0.33
+```
+This example implements a TCP echo server on port 1234. You can try connecting to it with:
+```
+nc 192.168.0.250 1234
+```
+Send it some data, you should see it echoed back and printed in the firmware's logs.
+
+## License
+
+This work is licensed under either of
+
+- Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or
+  <http://www.apache.org/licenses/LICENSE-2.0>)
+- MIT license ([LICENSE-MIT](LICENSE-MIT) or <http://opensource.org/licenses/MIT>)
+
+at your option.
+