Document and check the consistency of truncated MAC encodings

Add comments noting that the maximum length of a MAC must fit in
PSA_ALG_MAC_TRUNCATION_MASK. Add a unit test that verifies that the
maximum MAC size fits.
diff --git a/tests/suites/test_suite_psa_crypto.data b/tests/suites/test_suite_psa_crypto.data
index d8a5924..e8b119e 100644
--- a/tests/suites/test_suite_psa_crypto.data
+++ b/tests/suites/test_suite_psa_crypto.data
@@ -1,3 +1,6 @@
+PSA compile-time sanity checks
+static_checks:
+
 PSA init/deinit
 init_deinit: