Adds the Cortex-A53 CPU to the target architecture variant choice. This
sets the toolchain to use Cortex-A53 as the target. The effect is that
various Cortex-A53 tunings are enabled for the compilation of packages.
Signed-off-by: Matt Flax <flatmax@flatmax.org> Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com> Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr> Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>