add missing "enable" field to openssl feature

this ensures that an explicitly requested linked/runtime support is
complained about when the test fails. the old configure would do that as
well.

Change-Id: I7f235fa7df5e5d53938de0e32b07536447b8d1d4
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

configure.json

@@ -1609,6 +1609,7 @@
         },
         "openssl": {
             "description": "OpenSSL",
+            "enable": "input.openssl == 'yes' || input.openssl == 'linked' || input.openssl == 'runtime'",
             "condition": "!features.securetransport && tests.openssl",
             "output": [
                 { "type": "publicQtConfig", "condition": "!features.openssl-linked" },