kernel: Bump to 3.18.9

kernel: Align pcm512x driver with upstream
See: raspberrypi/linux#873

kernel: dts: overlay: add mz61581, fix piscreen and rpi-display
See: raspberrypi/linux#874

kernel: bcm2709: Increase the spare/free IRQs to match bcm2708
See: raspberrypi/linux#871

kernel: add support for Adafruit PiTFT
See: raspberrypi/linux#858

firmware: dispserve: Allow vsync requests from multiple clients
See: raspberrypi/userland#218

firmware: hello_fft: Update to version 3
See: http://www.aholme.co.uk/GPU_FFT/Main.htm

Author: popcornmix