Generate config file during build #515
Description
Produce a single file that contains all configs used for building, similar to coreboot's generated .config file.
This will allow inspecting/verifying configs without having to look at the verbose toolchain output.
(Based on this idea: also embed it into the flash so that it can be extracted and used to reproduce the build, similar to .config being included in the CBFS. But probably issues with flash space to do this?)
See also: #443