Merge "doc: DEVICE_*_MATRIX_FILE specifies absolute paths" am: cc6279316f am: 4e7d50fe01 am: dfb4a153dd

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/1455056

Change-Id: I14b3bde583ee09889dfe2390626505e6270d51ed