archiver: Configurable tarball compression

In order to be more efficient, we use xz as compression method
to create GPL sources archives.

Signed-off-by: Fabien Lahoudere <fabien.lahoudere@collabora.com>
[V1 was https://patchwork.openembedded.org/patch/155985/

]
[Rebased]
Signed-off-by: Ian Ray <ian.ray@ge.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>