fix(cpus): workaround for Cortex-A710 erratum 1916945

Cortex-A710 erratum 1916945 is a Cat B erratum that applies
to revisions r0p0 and r1p0 and is fixed in r2p0.

The workaround is to set CPUECTLR_EL1[8]. This has a slight
performance impact.

SDEN documentation:
https://developer.arm.com/documentation/SDEN1775101

Change-Id: I54793492c527928d7f266165a31b8613de838e69
Signed-off-by: John Powell <john.powell@arm.com>
diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index 8a99a58..643d3a4 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -577,6 +577,10 @@
    Cortex-A710 CPU. This needs to be enabled only for revision r1p0. It has
    been fixed in r2p0.
 
+-  ``ERRATA_A710_1916945``: This applies errata 1916945 workaround to
+   Cortex-A710 CPU. This needs to be enabled only for revisions r0p0 and r1p0.
+   It has been fixed in r2p0.
+
 -  ``ERRATA_A710_1987031``: This applies errata 1987031 workaround to
    Cortex-A710 CPU. This needs to be enabled only for revisions r0p0, r1p0 and
    r2p0 of the CPU. It is still open.