Add dependency to list of asset files

We had a dependency on each file in the asset directories, but that
wouldn't cause aapt2 to run if a file was removed.  Add a dependency
on a file that contains the list of files in the asset directories.

Fixes: 172867096
Test: m CarrierConfig && rm packages/apps/CarrierConfig/assets/carrier_config_no_sim.xml && m CarrierConfig
Change-Id: I35f3b85355fa890a3e95eaa6458a21466b6930e4