lib/cpu: Workaround for Cortex A77 erratum 1946167

Cortex A77 erratum 1946167 is a Cat B erratum that applies to revisions
<= r1p1. This erratum is avoided by inserting a DMB ST before acquire
atomic instructions without release semantics through a series of
writes to implementation defined system registers.

SDEN can be found here:
https://documentation-service.arm.com/static/600057a29b9c2d1bb22cd1be?token=

Signed-off-by: Lauren Wehrmeister <lauren.wehrmeister@arm.com>
Change-Id: I53e3b4fb7e7575ec83d75c2f132eda5ae0b4f01f
3 files changed