Add support for no-vendor-variant VNDK

When no-vendor-variant VNDK is enabled, the vendor variant of VNDK
libraries are not installed.  In this case, the vendor binaries need to
be able to link in the core variant.

Update the linker config so that we export such VNDK libraries to the
proper linker namespaces.

Bug: 119423884
Test: Enable no-vendor-variant VNDK for a dummy VNDK library.  Boot and
      check the vendor variant does not exist and only the core variant
      is used.

Change-Id: I71274fdf61373663603a5fbc3497400420094fcf