driver: Add driver for Dediprog SPI-flash emulator

[sjg20]

The EM100-pro is a SPI-flash emulator which supports a variety of chips. It can be used to provide an image to a booting system.

Add a driver which allows images to be loaded ready for use. Provide a trace facility for use when the board does not boot.

This emulator is widely used on x86 machines since they boot using SPI flash. It is prohibitively expensive (in terms of time) to re-flash the SPI chip on test run, whereas the Dediprog emulator updates in about 5 seconds.

This has been tested on several x86 Chromebooks, including coral.

• [X] Documentation for the feature
• [ ] Tests for the feature
• [X] The arguments and description in doc/configuration.rst have been updated
• [X] PR has been tested