wpa-supplicant: add options to enable the new DBus interface

Allow to configure the DBus interfaces that the wpa_supplicant
binary should support (old or new or both). Also allow to
enable introspection support on the new DBus interface.

Signed-off-by: Sven Neumann <s.neumann@raumfeld.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Tested-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
 (build-test with all features enabled)
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>