Camera: Fix client permission check

Modify StageFright's CameraSource to forward calling PID as
client PID when connecting to CameraService so CameraService
can check if the client PID has permission to use camera.

Change CameraService to check calling UID is trusted before
using the passed in client PID and client UID to verify permission.

Bug: 24511454
Change-Id: I4906ab73510e2c75714690bed675e3c13aca3ccf