4a-hal: Cleanup and 'haldependencies' feature

Cleanup 4a-hal repository.

Add 'haldependencies' functionnality :
'haldependencies' is a new section of hal configuration file. This new section will be used to probe for multiple audio device using only one hal. Each probed device could be 'mandatory', 'dynamic' (optional but periodically probed), or 'static' (optional and probed only at startup). The result of handling this section will be used by softmixer and
in 'halmap' section.