fix(cpus): workaround for Cortex-X3 erratum 2302506

Cortex-X3 erratum 2302506 is a cat B erratum that applies to
revisions r0p0-r1p1 and is fixed in r1p2. The workaround is to
set bit[0] of CPUACTLR2 which will force PLDW/PFRM ST to behave
like PLD/PRFM LD and not cause invalidation to other PE caches.

There might be a small performance degradation to this workaround
for certain workloads that share data.

SDEN can be found here:
https://developer.arm.com/documentation/2055130/latest

Change-Id: I048b830867915b88afa36582c6da05734a56d22a
Signed-off-by: Bipin Ravi <bipin.ravi@arm.com>
diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index 905b016..3a75dbd 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -771,6 +771,10 @@
   CPU. This needs to be enabled only for revisions r0p0, r1p0, r1p1 and r1p2 of
   the CPU and is still open.
 
+- ``ERRATA_X3_2302506``: This applies errata 2302506 workaround to the Cortex-X3
+  CPU. This needs to be enabled only for revisions r0p0, r1p0 and r1p1, it is
+  fixed in r1p2.
+
 - ``ERRATA_X3_2313909``: This applies errata 2313909 workaround to
   Cortex-X3 CPU. This needs to be enabled only for revisions r0p0 and r1p0
   of the CPU, it is fixed in r1p1.
@@ -946,7 +950,7 @@
 
 --------------
 
-*Copyright (c) 2014-2023, Arm Limited and Contributors. All rights reserved.*
+*Copyright (c) 2014-2024, Arm Limited and Contributors. All rights reserved.*
 
 .. _CVE-2017-5715: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-5715
 .. _CVE-2018-3639: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-3639