brillo_config: add missing mkdir for product rules

When doing a clean build, creating this file fails because the dir does
not yet exist:
echo "" > out/target/product/brilloemulator_arm/obj/ETC/product_id_intermediates/product_id
/bin/bash: out/target/product/brilloemulator_arm/obj/ETC/product_id_intermediates/product_id: No such file or directory

BUG: 24585672
Change-Id: I9c4a646b8d86cd303b0114f9b64d02896797f720
1 file changed