Allow building with linaro Cortex-A8 iptimized toolchain

Change-Id: I33ba135ea772b31fe0a8d2c36c8e99b5f0fdbd62
kernel build: add a new flag $(TARGET_KERNEL_CUSTOM_TOOLCHAIN_SUFFIX

Used to define the name of the binaries used to compile. Usually this is arm-eabi but with
custom toolchains this sometimes needs to be changed. Allow that to be done.

Must be used in conjunction with TARGET_KERNEL_CUSTOM_TOOLCHAIN

Change-Id: I4d6850c96573b5959dc421e0049c9fb7e88db105
build: Fallback to "arm-eabi-" if TARGET_KERNEL_CUSTOM_TOOLCHAIN_SUFFIX is not set

Change-Id: I8be1af2b0b9d03bfbef0483f2591ca8ef100a6c2
build: add modified envsetup script for compiling with linaro

(envsetup-linaro.sh)

Change-Id: I88860cb4638df6f41faae533ea7ec585a372482e