Introduce initial recipe for Softbus

Softbus implements "Distributed Communication Subsystem".
This commit provides initial recipe to build softbus
using bitbake and link it to the foundation application.

The functionality hasn't been tested (only build) so when
Softbus is actually used some missing bits may appear.

Signed-off-by: Zbigniew Bodek <zbigniew.bodek@huawei.com>