ESP32 spi slave mode

[bugadani]

Thank you for your contribution!

We appreciate the time and effort you've put into this pull request.
To help us review it efficiently, please ensure you've gone through the following checklist:

Submission Checklist 📝

• I have updated existing examples or added new ones (if applicable).
• I have used cargo xtask fmt-packages command to ensure that all changed code is formatted correctly.
• My changes were added to the CHANGELOG.md in the proper section.
• I have added necessary changes to user code to the Migration Guide.
• My changes are in accordance to the esp-rs API guidelines

Extra:

• I have read the CONTRIBUTING.md guide and followed its instructions.

Pull Request Details 📖

Description

The hardware has some difficulties with mode 0 and 2, so those aren't supported. According to the ESP-IDF docs we could make it work without DMA (and shovel FIFO contents into the buffer in interrupt handlers, for example).

Testing

Enabled the test case for ESP32, modified it to use Mode 1 and ran it locally (with a different pin assignment suitable for the Ethernet devkits I have).

Fixes #469