Add SYSTEM_CAMERA capability to camera2 and define @SystemApi SYSTEM_CAMERA permissions.

In order to access system-only cameras client processes need
SYSTEM_CAMERA permissions in addition to CAMERA permissions. A
permission was preferred over other mechanisms such as having private
connections would need to hard-code the package name(s) of clients using
system only camera devices. A system | signature permission on the other hand,
would make this more flexible and would be better for security.

Bug: 133508924

Test: cts CameraManagerTest, CameraDeviceTest
Test: Give cts test SYSTEM_CAMERA permissions by using
      adoptShellPermissions and run some camera tests.

Change-Id: Ibcd6ccdb231dcca949ed4fb14712d033a5801d36
Signed-off-by: Jayant Chowdhary <jchowdhary@google.com>