kbuild: rebuild initramfs if content of initramfs changes
initramfs.cpio.gz being build in usr/ and included in the
kernel was not rebuild when the included files changed.
To fix this the following was done:
- let gen_initramfs.sh generate a list of files and directories included
in the initramfs
- gen_initramfs generate the gzipped cpio archive so we could simplify
the kbuild file (Makefile)
- utilising the kbuild infrastructure so when uid/gid root mapping changes
the initramfs will be rebuild
With this change we have a much more robust initramfs generation.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>