Port  Tuna optimized VMSPLIT from fancy Kernel

By allocating more memory to the kernel (rather than userspace),
vmalloc can be increased without invoking highmem.

Signed-off-by: Willi Ye <williye97@gmail.com>

Conflicts:
	arch/arm/configs/gk_tuna_defconfig
	arch/arm/configs/tuna-tw_defconfig
	arch/arm/configs/tuna180_defconfig
	arch/arm/configs/tuna_defconfig