arch/arm: add armv8.1a cores

arch/arm: add armv8.1a cores

The armv8.1a generation is a cumulative extension to armv8a. It adds new
extensions, and makes some previously optional ones now mandatory.

Since gcc correctly enables the appropriate extensions based on the core
name, we don't really need to introduce a separate config for armv8.1a,
and we can piggyback on armv8a.

All those new cores are aarch64 only (gcc fails to build in arm mode).

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>