cameraserver: Modified rules for different kinds of system cameras.

Since we now have AIDL HALs as well, just depending on whether a binder
call is being made from a hwbinder thread is not enough to determine
whether a system camera / hidden secure camera should be accessible to the
client. The same goes for modifying oom scores / process state for
vendor clients. Instead we now allow privileged clients (uid <
AID_APP_START) to access system and hidden secure cameras. This will
include vendor clients as well. Oom score and process state re-mapping is now done for native
privileged clients.

Bug: 196432585

Test: Make Camera2 app privileged; make all cameras on device system only cameras
      See that other 3P apps / GCA can't access cameras; Camera2 can.

Test: CTS with cuttlefish depth camera made system camera

Test: Manually check that privileged native camera clients have their
      oom score and process state modified to let 3P apps evict them.

Test: atest Camera2PermissionTest.java

Change-Id: I1e81a554491f3d84f28d82a22bd0683a3407d46f
Signed-off-by: Jayant Chowdhary <jchowdhary@google.com>