No abi diffing for vndk libraries which are not vendor available.

Vendor binaries cannot directly link with vndk libraries which are not vendor
available. We don't need them to be abi stable.

Bug: 66301104

Test: cd external/cblas; touch src/cblas_cher.c; mm -j64 does not
      produce an lsdump for libblas, since it isn't vendor available,
      even though it is vndk_enabled: true.

Change-Id: Ib2e1eaa06c4dc2e05623bd7b9aa3a83010f76bd1