fix(cpus): workaround for Neoverse-N3 erratum 3699563

Neoverse-N3 erratum 3699563 that applies to r0p0 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-3050973/latest/

Change-Id: I77aaf8ae0afff3adde9a85f4a1a13ac9d1daf0af
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 a978d9b..f4c2312 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -732,6 +732,11 @@
    CPU. This needs to be enabled for revisions r0p0, r0p1, r0p2, r0p3 and is
    still open.
 
+For Neoverse N3, the following errata build flags are defined :
+
+-  ``ERRATA_N3_3699563``: This applies errata 3699563 workaround to Neoverse-N3
+   CPU. This needs to be enabled for revisions r0p0 and is still open.
+
 For Cortex-X2, the following errata build flags are defined :
 
 -  ``ERRATA_X2_2002765``: This applies errata 2002765 workaround to Cortex-X2