Modify update-metadata to be git aware

The Apertis update-metadata script has been created to aid developers who need to correctly update the kernels metadata when the kernel version is changed. The script currently works, but leaves it up to the developer to handle staging the changes in git to be merged. As we expect this script to only really be used in Apertis where the kernel will be in git, we can do a bit more and stage the regenerated files.

Signed-off-by: Martyn Welch martyn.welch@collabora.com