CI: add debug yml file for ease of use

There are cases where a developer might want to enable things, like
debug-tweaks, which are useful in their testing but not something we
would want in a production environment.  Create a file where these can
be added without affecting other things.

Signed-off-by: Jon Mason <jon.mason@arm.com>

ci/debug.yml

@@ -0,0 +1,7 @@
+header:
+  version: 11
+
+# Add universally helpful features when testing boards
+local_conf_header:
+  debug: |
+    EXTRA_IMAGE_FEATURES:append = " debug-tweaks"

ci/testimage.yml

@@ -1,9 +1,10 @@
 header:
   version: 11
+  includes:
+    - ci/debug.yml
 
 local_conf_header:
   testimage: |
-    EXTRA_IMAGE_FEATURES:append = " debug-tweaks"
     IMAGE_CLASSES += "testimage"
     TESTIMAGE_AUTO = "1"
   kvm: |