Final (?!?!?!) phone_car refactoring.

- Got rid of PHONE_car/device-common.mk
- Simplified PHONE_car/device-PHONE-car.mk so it just include other makefiles
- Moved computepipe.mk to common code

Fixes: 160823761
Test: built and booted the affected devices

Change-Id: I8557b3b81659f2ab24becf5c176f9d49d72dc581
16 files changed