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_internal.h b/library/psa_util_internal.h
index 3e62d5f..70a08a0 100644
--- a/library/psa_util_internal.h
+++ b/library/psa_util_internal.h
@@ -16,7 +16,7 @@
 
 #include "psa/crypto.h"
 
-#if defined(MBEDTLS_PSA_CRYPTO_C)
+#if defined(MBEDTLS_PSA_CRYPTO_CLIENT)
 
 /*************************************************************************
  * FFDH
@@ -96,5 +96,5 @@
                           sizeof(error_list)/sizeof(error_list[0]),   \
                           fallback_f)
 
-#endif /* MBEDTLS_PSA_CRYPTO_C */
+#endif /* MBEDTLS_PSA_CRYPTO_CLIENT */
 #endif /* MBEDTLS_PSA_UTIL_INTERNAL_H */