Make starlark board configuration work with sdk_phone_x86_64

The main issue with board configuration up till this
cl was that it didn't have access to the product configuration
variables. Pass those in by dumping the make variables to a
temporary file, which is then converted to RBC, loaded,
and passed to the starlark board config..

Bug: 201700692
Test: build/bazel/ci/rbc_product_config.sh -pb sdk_phone_x86_64-userdebug
Change-Id: I9a4946b970ca43c5b5f53a6c507ad2c1a2eca61e