nptl: Add copyright notice tst-sem11 and tst-sem12 tests

Add a copyright notice to the tst-sem11 and tst-sem12 tests, observing
that they have been originally contributed back in 2007, with commit
2af4e3e5 ("Test of semaphores.").
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>