Priority: required -> Priority: optional

Change-Id: Ia9df464ec40e2a9aeefb5ffc4f11a81721a07e36
diff --git a/debian/control b/debian/control
index cba36bb..6a06fc7 100644
--- a/debian/control
+++ b/debian/control
@@ -6,14 +6,14 @@
 
 Package: linux-image-4.9.51-aiy
 Section: misc
-Priority: required
+Priority: optional
 Architecture: arm64 armhf
 Depends: kmod, ${perl:Depends}
 Description: Linux kernel image for the AIY Board
 
 Package: linux-headers-4.9.51-aiy
 Section: misc
-Priority: required
+Priority: optional
 Architecture: arm64 armhf
 Depends: ${perl:Depends},
          linux-kbuild-4.9.51-aiy [${Arch}]
@@ -21,6 +21,6 @@
 
 Package: linux-kbuild-4.9.51-aiy
 Section: misc
-Priority: required
+Priority: optional
 Architecture: arm64 armhf
 Description: Linux kernel build tools for the AIY Board