Test: Secure side tests for the split build

TF-M builds as an external project feeded by TFM_TEST_REPO_PATH.
Having TFM_TEST_REPO_PATH in the build options, main TF-M repo adds
    add_subdirectory(${TFM_TEST_REPO_PATH}/tests)
to include testing compoannent on secure side.

Signed-off-by: Anton Komlev <anton.komlev@arm.com>
Change-Id: Id9c4db3031aa266ff408ac932bd62bbd3d8dd079
25 files changed