tools: Fall back to importlib_resources on Python 3.6

importlib.resources became part of 3.7 only. Allow using distros with
3.6 and the importlib_resources backport.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/__main__.py b/tools/patman/__main__.py
index 48ffbc8..8eba5d3 100755
--- a/tools/patman/__main__.py
+++ b/tools/patman/__main__.py
@@ -7,7 +7,11 @@
 """See README for more information"""
 
 from argparse import ArgumentParser
-import importlib.resources
+try:
+    import importlib.resources
+except ImportError:
+    # for Python 3.6
+    import importlib_resources
 import os
 import re
 import sys