tools: Add find_secure_image function

- Used by Non-secure targets post-build hooks to find
  the relevant secure image.

Author: Michael Schwarcz

tools/psa/__init__.py

@@ -0,0 +1,16 @@
+from os.path import basename
+
+
+def find_secure_image(notify, resources, ns_image_path, configured_s_image_path, image_type):
+    """ Find secure image. """
+    image_files = resources.get_file_paths(image_type)
+    secure_image = next((f for f in image_files if basename(f) == configured_s_image_path), None)
+    secure_image = next((f for f in image_files if basename(f) == basename(ns_image_path)), secure_image)
+
+    if secure_image:
+        notify.debug("Secure image file found: %s." % secure_image)
+    else:
+        notify.debug("Secure image file %s not found. Aborting." % configured_s_image_path)
+        raise Exception("Required secure image not found.")
+
+    return secure_image