buildroot

arch/arm: add some non-cortex armv8a cores

Some need gcc-5, some gcc-6 and some gcc-7.

The thunderx familly does not build in 32-bit mode (gcc complains
that the CPU is unknown, and even gcc master only knows them as
aarch64-only).

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>