[AUDIO] When setting a null device for an audio output, force the next routing request.

When a null device is set for an audio ouput, the outputDesc->mDevice is not updated,
thus the routing update is not done next time the device is selected for that output.
To meet the device change conditions, a boolean member mForceRouting has been
introduced to force the routing next time the output is set with a non-null device.

Change-Id: I95c6c3fb85dd6c229737739d111b08fa2f7d826b
Author: Vincent Becker <vincentx.becker@intel.com>
Signed-off-by: Vincent Becker <vincentx.becker@intel.com>
Signed-off-by: Zhi Jin <zhi.jin@intel.com>
Signed-off-by: Shuo Gao <shuo.gao@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>
Signed-off-by: Jack Ren <jack.ren@intel.com>
Author-tracking-BZ: 53856