DO NOT MERGE: Add a way to allow untrusted_apps to talk to halserver domains

Vendor HAL extentsions are currently allowed to discover hardware
services that are labelled with 'untrusted_app_visible_hwservice'.
However, the policy doesn't allow these apps to talk to these services.
This CL makes sure that is now possible via the
'untrusted_app_visible_halserver' attribute for vendor domains that host
such a service.

Bug: 64382381
Test: Boot device and observe no new denials.

Change-Id: I1ffc1a62bdf7506a311f5a19acdab8c7caec902b
Signed-off-by: Sandeep Patil <sspatil@google.com>