test: Support an init/uninit functions for test suites

test: Support an init/uninit functions for test suites

Some suites need things to be set up before they can run. Add a way to
declare an init function using the UNIT_TEST_INIT() macro. The init
function is just like any other test, but is always placed first so that
it runs before all the other test functions in the suite.

Add an uninit function as well, to clean up after the test.

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