Juno/vexpress Android kernel based on 3.18 version of Linaro Stable Kernel (LSK)

Changes in this version:
- Add some SCPI stress test code (drivers/firmware/arm_scpi_test.c)
- Updated Juno idle state params to match values recently suggested by
  Lorenzo (http://www.spinics.net/lists/arm-kernel/msg462932.html)
- Update to 15.12 release of LSK 3.18. This brings in backports of
  Privileged Access Never (PAN) and OF Overlay (a device-tree feature)
- Update to latest Android LSK branch, this brings in new AOSP code.