modules: tf-m: fix unused CMake variable warning

Define and pass down PSA_ARCH_TESTS_PATH only in the sample that
needs it (tfm_psa_test).
Otherwise, it provokes a CMake warning because the variable does not
get used in TF-M.

Signed-off-by: Tomi Fontanilles <tomi.fontanilles@nordicsemi.no>
2 files changed