Match src paths with aidl package name

In order for the build system to track updates to the header files
during incremental builds, always specify the src files using the same
path as the package for C++ compilations.

Bug: 112114177
Test: m
Change-Id: I5fb25124a26f190c462e2e60fc75a88d48643c10
Merged-In: I5fb25124a26f190c462e2e60fc75a88d48643c10