audio policy: engine configurable: allow to use custom PFW and plugins

Android build system prevents from having the same module
target refered in more than one makefile. Some platform may need to use
a custom parameter manager version than the aosp version of the PFW.
It also concerns with associated plugins.

This patch inhibits the AOSP Policy PFW plugin if USE_CUSTOM_PARAMETER_MANAGER is
set to true.

Bug; 22887211

Change-Id: I71147b3e7c8a9296af3182f8a1401bc37191a276
Signed-off-by: François Gaffie <francois.gaffie@intel.com>