Switch to 'update.zip' for updates

This avoids some updates only needing an updated rootfs, while
others require a kernel and initramfs update as well. Now, the
user just needs to extract this update.zip file to the root of
their SD card.

.gitlab-ci.yml

@@ -30,7 +30,7 @@ make-image:
     name: "sdimage-$CI_COMMIT_SHA"
     paths:
     - sdcard.img.zip
-    - rootfs.squashfs
+    - update.zip
     - build.log
     when: always
   cache:

Makefile

@@ -40,8 +40,9 @@ else
 endif
 	git submodule > buildroot/output/.cache-version
 	zip -j sdcard.img.zip buildroot/output/images/sdcard.img
-	cp buildroot/output/images/rootfs.squashfs .
-
+	zip -j update.zip buildroot/output/images/zImage \
+	                  buildroot/output/images/rootfs.squashfs \
+	                  buildroot/output/images/initramfs.cpio.lzo
 .PHONY: update-config
 update-config:
 	cd "$(CURDIR)/buildroot" && cp "configs/piso_defconfig" ".config"