Audio Policy: engine configurable: remove sign bit from conf files

In order to avoid mistake or extra configuration, this patch removes
from xml/pfw configuration files the sign bit for input device and adds
it programmaticaly within the Parameter Framework policy plugin

Bug: 25075342

Change-Id: I571e8ae882cb338330d6a10da309b1249ce0417e
Signed-off-by: François Gaffie <francois.gaffie@intel.com>