VC4 GPU Build

Raspberry Pi 2 default build is now VC4 GPU enabled.

Follow README of https://github.com/peyo-hd/local_manifests & https://github.com/peyo-hd/device_brcm_rpi2

For vc4 original work of Eric Anholt, refer to http://dri.freedesktop.org/wiki/VC4 And his github : https://github.com/anholt

How to assign more memory to GPU

Among 1GB DRAM on Rpi2 board, amount of GPU side memory could be changed with CONFIG_CMA_SIZE_MBYTES in the file - kernel/rpi/arch/arm/configs/bcm2709_defconfig

Current value is 256. It could be increased to 320 or more. But there is critical side-effect of ARM side memory reduction. Android could suffer from frequent Out-of-Memory.