Phony module vndk_package is added

This phony module aggregates all the VNDK-related libraries so that they
can be installed to the system partition simply by adding 'vndk_package'
to PRODUCT_PACKAGES. This is to sneure that all VNDK libraries are
installed even when there is no vendor library using some of the VNDK
libs (especially when building system image only).

Bug: 64013660
Test: BOARD_VNDK_VERSION=current m -j vndk_package
Change-Id: I3a14a7eaaffd6a7f3258a4be59b1c5813153714d