This adds mediacodec to the list of temporary exemptions from the "no
Binder in vendor" rule.

Test: mmm system/sepolicy
Bug: 35870313
Change-Id: I0f00d4bfb90d6da45ae2fed65864bb8fb0a4e78e

Test: Camera, Photos, YouTube and Play Movies apps.
Bug: 35328855
Change-Id: I3643b668817a7336f7ccda781734920fbbcc2c63

Divide policy into public and private components.  This is the first
step in splitting the policy creation for platform and non-platform
policies.  The policy in the public directory will be exported for use
in non-platform policy creation.  Backwards compatibility with it will
be achieved by converting the exported policy into attribute-based
policy when included as part of the non-platform policy and a mapping
file will be maintained to be included with the platform policy that
maps exported attributes of previous versions to the current platform
version.

Eventually we would like to create a clear interface between the
platform and non-platform device components so that the exported policy,
and the need for attributes is minimal.  For now, almost all types and
avrules are left in public.

Test: Tested by building policy and running on device.

Change-Id: Idef796c9ec169259787c3f9d8f423edf4ce27f8c