Add PRODUCT_EXTRA_VNDK_VERSIONS product variables

PRODUCT_EXTRA_VNDK_VERSIONS should be in _product_list_vars
because it's used as a list with probably more than one version
included/set in differemt makefiles.

Bug: 132046980
Test: $ lunch aosp_x86_ab-userdebug
      $ m -j
      $ find $OUT/system/ -name vndk-* # vndk-27 directory is included

Change-Id: Iee9b7b678a23eed781cc761d820db9ff67ae5d34