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: I33c684de4c0c52012b496d2f2447eceaba26c191
Merged-In: I33c684de4c0c52012b496d2f2447eceaba26c191