Merge "Rename mainline_system(.*).mk to generic_system(.*).mk" into...

Merge "Rename mainline_system(.*).mk to generic_system(.*).mk" into rvc-dev-plus-aosp am: 147c8950 am: c75de1fd

Original change: https://googleplex-android-review.googlesource.com/c/platform/build/+/12344111

Change-Id: I420f5d490d80504b368f981ca2a021cf6d1d1eb2