[FEATURE] Drop Cmocka unit tests dependence on XTOS CMake files

[singalsu]

Is your feature request related to a problem? Please describe.
The test/cmocka/CMakeLists.txt needs an non-existing XTOS header src/arch/xtos-wrapper/include.
We can't run xtensa unit tests.

Describe the solution you'd like
Platform independent generic headers to replace XTOS header would be needed for cmocka minimum needs.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[marc-hb]

Thanks @singalsu for filing this! Any idea how "hard" is the dependency on XTOS headers and CMake files? Days or weeks of work?

I think it's good to have this file in in sof-test because that's where we file and triage most of our test coverage gaps but all the corresponding code is in the main sof repo and should stay there.