cameraserver: Add support for system only cameras

Bug: 133508924
Bug: 138135733

android.permission.CAMERA and android.permission.SYSTEM_CAMERA are both
required by a client process to access system only cameras.

Test: Advertise the back camera as system only;
        1) don't give Camera2 SYSTEM_CAMERA permissions,
           Camera2 can't connect to the back camera
        2) give Camera2 SYSTEM_CAMERA permissions, Camera2 successfully
           connects.
        3) 3P app can't connect to any camera if all cameras are
           advertised as SYSTEM_ONLY_CAMERAs.

Test: CTS CameraDeviceTest, CameraManagerTest

Change-Id: I0309462f962d9c8c92564ef6781b2aae1485a933
Signed-off-by: Jayant Chowdhary <jchowdhary@google.com>