audiohal: Fix UAF of HAL devices in Stream objects

Stream objects used to hold a pointer to underlying HAL device
object which they didn't own. Since destruction of server side
objects is asynchronous, it was possible that a Device object
gets destroyed before Stream objects, making all the HAL device
object pointer to become stale.

Fixed by adding a strong reference to Device objects into Stream
objects.

Bug: 36702804
Change-Id: I3da3611afbb91d6fd6410ac5b8af2a2eebfa6dac
Test: ran Loopback app and HAL VTS tests
(cherry picked from commit 96d3573c)