audiopolicy: engineconfigurable: continue switching to bp

This CL adds genrule_defaults target to allows getting rid of mk
for configuration files generation.

Test: build & boot
Change-Id: Ida4ec17ab3e67788b512b95ac8d2c0f4c530014a
Signed-off-by: Francois Gaffie <francois.gaffie@renault.com>