kunit: defconfig: add defconfigs for building KUnit tests Add defconfig for UML and a fragment that can be used to configure other architectures for building KUnit tests. Add option to kunit_tool to use a defconfig to create the kunitconfig. Signed-off-by: Brendan Higgins <brendanhiggins@google.com> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Reviewed-by: Logan Gunthorpe <logang@deltatee.com>