Deprecate MBEDTLS_PKCS11_C feature
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 058969b..789ba5b 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -2814,6 +2814,9 @@
  *
  * Enable wrapper for PKCS#11 smartcard support.
  *
+ * \deprecated This option is deprecated and will likely be removed in a
+ *             future version of Mbed TLS.
+ *
  * Module:  library/pkcs11.c
  * Caller:  library/pk.c
  *