VR: Add sepolicy for VR HWC service

VR HWC is being split out of VR Window Manager. It creates a HW binder
interface used by SurfaceFlinger which implements the HWComposer HAL and
a regular binder interface which will be used by a system app to receive
the SurfaceFlinger output.

Bug: b/36051907
Test: Ran in permissive mode and ensured no permission errors show in
logcat.

Change-Id: If1360bc8fa339a80100124c4e89e69c64b29d2ae