deb-pkg: add source package

deb-pkg: add source package

Make deb-pkg build both source and binary package like make rpm-pkg does.
For people who only need binary kernel package, there is now bindeb-pkg
target, same target also used to build the .deb files if built from the
source package using dpkg-buildpackage.

Generated source package will build the same kernel .config than what
was available for make deb-pkg. The name of the source package can
be set with KDEB_SOURCENAME enviroment variable.

The source package is useful for GPL compliance, or for feeding to a
automated debian package builder.

Cc: Chris J Arges <[email protected]>
Reviewed-by: maximilian attems <[email protected]>
Reviewed-by: Ben Hutchings <[email protected]>
Signed-off-by: Riku Voipio <[email protected]>
Signed-off-by: Michal Marek <[email protected]>