errata: workaround for Neoverse V1 errata 1791573

Neoverse V1 erratum 1791573 is a Cat B erratum present in r0p0 and
r1p0 of the V1 processor core. It is fixed in r1p1.

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

Signed-off-by: John Powell <john.powell@arm.com>
Change-Id: Ic6f92da4d0b995bd04ca5b1673ffeedaebb71d10
diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index ab638fb..8d17d35 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -323,6 +323,12 @@
    CPU. This needs to be enabled for revisions r3p0, r3p1, r4p0, and r4p1, for
    revisions r0p0, r1p0, and r2p0 there is no workaround.
 
+For Neoverse V1, the following errata build flags are defined :
+
+-  ``ERRATA_V1_1791573``: This applies errata 1791573 workaround to Neoverse-V1
+   CPU. This needs to be enabled only for revisions r0p0 and r1p0, it is fixed
+   in r1p1.
+
 DSU Errata Workarounds
 ----------------------