errata: workaround for Neoverse N2 erratum 2067956

Neoverse N2 erratum 2067956 is a Cat B erratum that applies to
revision r0p0 and is still open. The workaround is to set
CPUACTLR_EL1[46] to force L2 tag ECC inline correction mode.
This workaround works on revision r0p0.

SDEN can be found here:
https://developer.arm.com/documentation/SDEN1982442/latest

Signed-off-by: Bipin Ravi <bipin.ravi@arm.com>
Change-Id: Ie92d18a379c66675b5c1c50fd0b8dde130848b21
diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index 9b8b0be..1f99892 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -378,6 +378,11 @@
    Cortex-A710 CPU. This needs to be enabled only for revisions r0p0, r1p0 and
    r2p0 of the CPU. It is still open.
 
+For Neoverse N2, the following errata build flags are defined :
+
+-  ``ERRATA_N2_2067956``: This applies errata 2067956 workaround to Neoverse-N2
+   CPU. This needs to be enabled for revision r0p0 of the CPU and is still open.
+
 DSU Errata Workarounds
 ----------------------