test: Add some tests for kconfig.h

The macros in this file are a little confusing and we currently have no
tests to check that they work as expected.

Add some tests which check the macros in C code. Add a few tests which
check that the build errors are generated correctly too, using buildman's
-a option.

Signed-off-by: Simon Glass <sjg@chromium.org>
7 files changed