Install VNDK_USING_CORE_VARIANT_LIBRARIES

With TARGET_VNDK_USE_CORE_VARIANT := true, some VNDK libraries are not
installed and instead system variants are used at runtime.

When building system only, VNDK_USING_CORE_VARIANT_LIBRARIES are not
installed under /system because there is no dependency to trigger
installing. (By definition, /vendor modules depends on vndk libs)

Bug: 148803529
Test: lunch aosp_cf_x86_go_phone-userdebug
      m systemimage # should install vndk libraries of core variant

Change-Id: Ied4347969955491b13dc674f2e8453d76592d1d7