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

ocontexts was split up into 4 files:
1.fs_use
2.genfs_contexts
3.initial_sid_contexts
4.port_contexts

Each file has their respective declerations in them.
Devices, in their respective device directory, can now specify sepolicy.fs_use, sepolicy.genfs_contexts, sepolicy.port_contexts, and sepolicy.initial_sid_contexts. These declerations will be added right behind their respective sepolicy counterparts in the concatenated configuration file.