Enable mic & camera by default

This CL sets the default value of device config for camera and mic (when
the setting hasn't been set before) as true.

Test: atest com.android.systemui.privacy
Test: manual
Bug: 168209929
Change-Id: I71107c692e1e7e6beea355ffa51317584f2b6e7c
Merged-In: I71107c692e1e7e6beea355ffa51317584f2b6e7c
(cherry picked from commit 22e8b46a)