CI: Replace unmigrated symbol test with non-Kconfig introduction test

Now that all symbols have been migrated to Kconfig, or are part of the
CFG namespace we do not need a complex check for unmigrated CONFIG
symbols. Any instance of #define (or #undef) or a CONFIG value is wrong,
so cause CI to fail.

This test is not as strict as possible yet as we have more symbols that
were not previously caught to deal with.

Signed-off-by: Tom Rini <trini@konsulko.com>