Currently meta-zephyr only checks out a subset of the kernel source.
With the addition of being able to generate machine configs from
zephyr source, we need to be able to have the complete source if we
don't want things to break badly.

Signed-off-by: Eilís Ní Fhlannagáin <elizabeth.flanagan@huawei.com>
Signed-off-by: Naveen Saini <naveen.kumar.saini@intel.com>