fix(cpus): workaround for Cortex-X3 erratum 3701769

Cortex-X3 erratum 3701769 that applies to r0p0, r1p0, r1p1 and r1p2
is still Open.

The workaround is for EL3 software that performs context save/restore
on a change of Security state to use a value of SCR_EL3.NS when
accessing ICH_VMCR_EL2 that reflects the Security state that owns the
data being saved or restored.

SDEN documentation:
https://developer.arm.com/documentation/SDEN-2055130/latest/

Change-Id: Ifd722e1bb8616ada2ad158297a7ca80b19a3370b
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index 00cfe19..5862f67 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -833,6 +833,10 @@
   CPU. This needs to be enabled only for revisions r0p0, r1p0 and r1p1 of the
   CPU. It is fixed in r1p2.
 
+- ``ERRATA_X3_3701769``: This applies errata 3701769 workaround to Cortex-X3
+  CPU. This needs to be enabled only for revisions r0p0, r1p0, r1p1 and r1p2
+  of the CPU and it is still open.
+
 For Cortex-X4, the following errata build flags are defined :
 
 - ``ERRATA_X4_2701112``: This applies erratum 2701112 workaround to Cortex-X4