Set PRODUCT_PRODUCT_VNDK_VERSION from product_config.mk

As a product variable, PRODUCT_PRODUCT_VNDK_VERSION cannot be defined
in config.mk. Instead it can be defined from product_config.mk.

Bug: 144534640
Test: check if the following command returns empty value
      $ PRODUCT_USE_PRODUCT_VNDK_OVERRIDE=false \
        get_build_var PRODUCT_PRODUCT_VNDK_VERSION
Change-Id: I304fb980610aec1dd5da05864b4c137997fc9aff