Update toolchain urls to 5.3-2016.05, which has support of ARMv8.1 arch
features, enabled by default on some setups with linux kernel v4.9 (rpi3)

ARMv8.1 architectural features in linux kernel:
CONFIG_ARM64_HW_AFDBM
CONFIG_ARM64_PAN
CONFIG_ARM64_LSE_ATOMICS
CONFIG_ARM64_VHE

Signed-off-by: Igor Opaniuk <igor.opaniuk@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>