kunit: tool: Add list of all valid test configs on UML

It's often desirable (particularly in test automation) to run as many
tests as possible. This config enables all the tests which work as
builtins under UML at present, increasing the total tests run from 156
to 342 (not counting 36 'skipped' tests).

They can be run with:
./tools/testing/kunit/kunit.py run
--kunitconfig=./tools/testing/kunit/configs/all_tests_uml.config

This acts as an in-between point between the KUNIT_ALL_TESTS config
(which enables only tests whose dependencies are already enabled), and
the kunit_tool --alltests option, which tries to use allyesconfig,
taking a very long time to build and breaking very often.

Signed-off-by: David Gow <davidgow@google.com>
Tested-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>