If a file exists in the initramfs at runtime, cpio won't overwrite it
by default when extracting the initramfs-extra archive. This adds the -u
option to cpio, to overwrite any existing files in the destination.
This is meant to fix issues where the -extra archive has an app that is
meant to replace a busybox app, busybox --install creates it in the
initramfs and gzip will skip it since it's newer than what is in the
archive.
cfed09ca36