Shorten encoding of version features

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/scripts/data_files/version_features.fmt b/scripts/data_files/version_features.fmt
index d3217a1..0e40597 100644
--- a/scripts/data_files/version_features.fmt
+++ b/scripts/data_files/version_features.fmt
@@ -44,6 +44,12 @@
         return -1;
     }
 
+    if (strncmp(feature, "MBEDTLS_", 8)) {
+        return -1;
+    }
+
+    feature += 8;
+
     while (*idx != NULL) {
         if (!strcmp(*idx, feature)) {
             return 0;