buildroot

toolchain-external: bump version of Linaro AArch64 toolchain

Tested with Qemu 2.6.1 and qemu_aarch64_virt_defconfig.
As reported by Gustavo Zacarias, this defconfig is known to fail with qemu
versions lower than 2.6.0.

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>