fix(cpus): workaround for Cortex-X4 erratum 2816013

Cortex-X4 erratum 2816013 is a Cat B erratum that applies
to all revisions <= r0p1 and is fixed in r0p2. This erratum
is only present when memory tagging is enabled.

The workaround is to set CPUACTLR5_EL1[14] to 1.

SDEN documentation:
https://developer.arm.com/documentation/SDEN-2432808/latest

Change-Id: I546044bde6e5eedd0abf61643d25e2dd2036df5c
Signed-off-by: Sona Mathew <sonarebecca.mathew@arm.com>
diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index 6147c1f..f253cd3 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -833,6 +833,9 @@
 - ``ERRATA_X4_2763018``: This applies errata 2763018 workaround to Cortex-X4
   CPU. This needs to be enabled for revisions r0p0 and r0p1. It is fixed in r0p2.
 
+- ``ERRATA_X4_2816013``: This applies errata 2816013 workaround to Cortex-X4
+  CPU. This needs to be enabled for revisions r0p0 and r0p1. It is fixed in r0p2.
+
 For Cortex-A510, the following errata build flags are defined :
 
 -  ``ERRATA_A510_1922240``: This applies errata 1922240 workaround to