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/library/psa_util.c b/library/psa_util.c
index 7384bf1..4ccc5b0 100644
--- a/library/psa_util.c
+++ b/library/psa_util.c
@@ -18,7 +18,7 @@
 
 #include "psa_util_internal.h"
 
-#if defined(MBEDTLS_PSA_CRYPTO_C)
+#if defined(MBEDTLS_PSA_CRYPTO_CLIENT)
 
 #include <psa/crypto.h>
 
@@ -363,7 +363,7 @@
     }
 }
 
-#endif /* MBEDTLS_PSA_CRYPTO_C */
+#endif /* MBEDTLS_PSA_CRYPTO_CLIENT */
 
 #if defined(MBEDTLS_PSA_UTIL_HAVE_ECDSA)