image-uboot: Use the Debos kernel commandline management tools

Use the `{setup,append}-kernel-cmdline` properties from the
`filesystem-deploy` Debos action to configure the commandline parameters
for the Linux kernel, rather than setting them by hand via sed.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>

apertis-image-uboot.yaml

@@ -75,13 +75,10 @@ actions:
         end: -4M
 
   - action: filesystem-deploy
+    setup-kernel-cmdline: true
+    append-kernel-cmdline: $cmdline
     description: Deploying ospack onto image
 
-  - action: run
-    description: Add kernel parameters
-    chroot: true
-    command: sed -i '1 s/$/{{ $cmdline }}/' /etc/kernel/cmdline
-
   - action: apt
     description: Kernel and system packages
     packages: