Explicitly use python3 everywhere

configs/swerv_config_gen.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 from fusesoc.capi2.generator import Generator
 import os
 import shutil

swerv_el2.core

@@ -85,7 +85,7 @@ generate:
 
 generators:
   swerv_el2_config:
-    interpreter: python
+    interpreter: python3
     command: configs/swerv_config_gen.py
     description : Create a SweRV EL2 configuration. Note! Only supports the default config