Add section/priority for source package

Change-Id: I5c3bf5f6b48b98c65e089cfd9b262f8596de0d15

debian/control

diff --git a/debian/control b/debian/control
index cb4fee7..e811fc9 100644
--- a/debian/control
+++ b/debian/control
@@ -1,6 +1,8 @@
 Source: imx-mkimage
 Maintainer: AIY Projects <support-aiyprojects@google.com>
 Build-Depends: debhelper
+Section: misc
+Priority: optional
 
 Package: imx-mkimage
 Section: misc