g2: add optimizations

-more cortex-a15 optimizing
-some misc optimization
-some credits to houston
-use 4.8 kernel toolchain, I'll add support for it in a few minutes
ps2: remove duplicate thing

Conflicts:
	BoardConfigCommon.mk

Change-Id: Iea8a67422f6ae6bf004d222a249e5783465a1cec