kunit: add kunit/Kconfig and <kunit/test.h> to ease upgrade from alpha

Provide macros to allow using KUNIT_EXPECT_EQ instead of EXPECT_EQ, etc.
And add a Kconfig to allow users to modernize their KConfig.

Update the example and template tests.

With this, the code can compile with a kunitconfig of
which is exactly what the upstream version would use.

Unfortunately we can't have "struct kunit" map back to "struct test"
Stuff that isn't upstream like <test/mock.h> wasn't touched.

This should hopefully make it easier for alpha users to do partial,
simple migrations now.
And it should make it a bit clearer what's not upstream.

Change-Id: I9b13a871e527125e40969beefbc939f4c9e0801d
5 files changed