Disable non-AOSP nnapi extensions on product partition in GSI

The extensions is for OEM. To avoid AOSP code using OEM
extensions mistakenly. GSI denys product to use the extensions
by enabling the following property:

    ro.nnapi.extensions.deny_on_product=true


Bug: 129900377
Test: make gsi_arm64-userdebug, check /system/build.prop
Change-Id: Ia679f1f9c108bd5a164c8cdeb1d73f57da755608