errata: workaround for Neoverse V1 errata 1966096

Neoverse V1 erratum 1966096 is a Cat B erratum present in the V1
processor core.  This issue is present in revisions r0p0, r1p0,
and r1p1, but the workaround only applies to r1p0 and r1p1, it is still
open.

SDEN can be found here:
https://documentation-service.arm.com/static/60d499080320e92fa40b4625

Signed-off-by: John Powell <john.powell@arm.com>
Change-Id: Ic0b9a931e38da8a7000648e221481e17c253563b
diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index aa1a247..4d7b179 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -344,6 +344,11 @@
    CPU. This needs to be enabled only for revision r1p0 and r1p1 of the
    CPU.
 
+-  ``ERRATA_V1_1966096``: This applies errata 1966096 workaround to Neoverse-V1
+   CPU. This needs to be enabled for revisions r1p0 and r1p1 of the CPU, the
+   issue is present in r0p0 as well but there is no workaround for that
+   revision.  It is still open.
+
 DSU Errata Workarounds
 ----------------------