scripts/checkpatch: more checks on files imported from Linux

scripts/checkpatch: more checks on files imported from Linux

If a file imported from Linux is touched, emit a warning and suggest
using scripts/update-linux-headers.sh.

Also check that updating imported files from Linux are not mixed with
other changes, in which case emit an error.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20240718072050.9503-1-sgarzare@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240813202329.1237572-7-alex.bennee@linaro.org>