Merge aconfig files per-module

Passing the list of all transitive aconfig files to Make causes extra
Kati analysis runs when dependencies are changed in Android.bp files.
Since Make is going to merge them anyways, merge them per-module and
pass a single aconfig file to Make for each module.

Fixes: 313698230
Test: m out/target/product/vsoc_x86_64/system/etc/aconfig_flags.pb
Change-Id: Ifde4826bc93bc06e40338f72b4cb39eed26ca08d