[automerger skipped] Merge "Rename mainline_system(.*).mk to generic_system(.*).mk" am: 84b82254 am: df762465 -s ours

am skip reason: Change-Id I3609ec2d91b0f08859a36cac75c25876b1db6d6a with SHA-1 0116b6cb is in history

Original change: https://android-review.googlesource.com/c/platform/build/+/1396210

Change-Id: I2c12890995dce0e62b0d7256b11e6078178e293c