tests: drivers: counter: add user mode test

Add a single counter API test case (not using callbacks) running in
user mode. Convert the existing test setup to use semaphores for
counting events to be able to utilize the same test setup and teardown
functionality in both user and supervisor mode tests.

Most of the counter API basic test suite still needs to run in
supervisor mode due the use of callback functions.

Signed-off-by: Henrik Brix Andersen <henrik@brixandersen.dk>