Align tests/src and include/src with 3.6 version

Allow tests/src and include/src to be Mbed TLS version-agnostic by:
* Sometimes accepting both an MBEDTLS_ and a PSA_ config option
* Sometimes using the version number to gate alternatives

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/tests/src/psa_exercise_key.c b/tests/src/psa_exercise_key.c
index ee83997..a496de0 100644
--- a/tests/src/psa_exercise_key.c
+++ b/tests/src/psa_exercise_key.c
@@ -11,7 +11,9 @@
 #include <test/macros.h>
 #include <test/psa_exercise_key.h>
 
-#if defined(MBEDTLS_PSA_CRYPTO_CLIENT)
+#if ((MBEDTLS_VERSION_MAJOR < 4) \
+    && defined(MBEDTLS_PSA_CRYPTO_C)) \
+    || defined(MBEDTLS_PSA_CRYPTO_CLIENT)
 
 #include <mbedtls/asn1.h>
 #include <psa/crypto.h>
@@ -1332,4 +1334,4 @@
 }
 #endif /* MBEDTLS_PK_C */
 
-#endif /* MBEDTLS_PSA_CRYPTO_CLIENT */
+#endif /* MBEDTLS_PSA_CRYPTO_C || MBEDTLS_PSA_CRYPTO_CLIENT */