tests: add new Doxygen tags to threads tests

Reason is that some threads tests have poor description Doxygen
tags. I decided to fix that situation in some tests which understand.

Update Doxygen tags for the next tests:
test_create_new_supervisor_thread_from_user()
test_user_mode_enter()
test_create_new_higher_prio_thread_from_user()
test_create_new_thread_from_user_huge_stacksize()

Signed-off-by: Maksim Masalski <maksim.masalski@intel.com>