Define its own UniquePtr in gatekeeper namespace

UniquePtr is deprecated and will be removed in a near future. Adding
own UniquePtr.h for gatekeeper.

This gatekeeper/UniquePtr.h is copied from global shared lib in Trusty.

Bug: 63686260
Bug: 63866913
Test: build with BOARD_VNDK_VERSION=current and boot
Merged-In: Ibe3bfd39e2381bb0c4a510abd28e1d8cc0eced72
Change-Id: Ibe3bfd39e2381bb0c4a510abd28e1d8cc0eced72
(cherry picked from commit 002c8667ef19be4b80ef7079a3a5cfb4ca85038c)
5 files changed