psa_util: change guard for mbedtls_psa_get_random() to CRYPTO_CLIENT

This commit also:
- updates changelog
- add a stub function to be used in component_test_psa_crypto_client()
  test

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/include/mbedtls/psa_util.h b/include/mbedtls/psa_util.h
index f79178d..c78cc23 100644
--- a/include/mbedtls/psa_util.h
+++ b/include/mbedtls/psa_util.h
@@ -21,7 +21,7 @@
  * otherwise error codes would be unknown in test_suite_psa_crypto_util.data.*/
 #include <mbedtls/asn1write.h>
 
-#if defined(MBEDTLS_PSA_CRYPTO_C)
+#if defined(MBEDTLS_PSA_CRYPTO_CLIENT)
 
 /** The random generator function for the PSA subsystem.
  *
@@ -139,7 +139,7 @@
 {
     return (mbedtls_md_type_t) (psa_alg & PSA_ALG_HASH_MASK);
 }
-#endif /* MBEDTLS_PSA_CRYPTO_C */
+#endif /* MBEDTLS_PSA_CRYPTO_CLIENT */
 
 #if defined(MBEDTLS_PSA_UTIL_HAVE_ECDSA)