fix(cpus): workaround for Neoverse N2 erratum 2779511

Neoverse N2 erratum 2779511 is a Cat B erratum that applies to
all revisions <=r0p2 and is fixed in r0p3. The workaround is to
set bit[47] of CPUACTLR3_EL1

SDEN documentation:
https://developer.arm.com/documentation/SDEN1982442/latest

Signed-off-by: Arvind Ram Prakash <arvind.ramprakash@arm.com>
Change-Id: Iaa0e30de8473ecb1df1fcca3a45904aac2e419b3
(cherry picked from commit 12d28067c9e76a78b148ed6fb94faf96de5e8502)
diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index 2945594..69d3722 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -655,6 +655,10 @@
    interconnect IP. This needs to be enabled for revisions r0p0, r0p1 and r0p2.
    It is fixed in r0p3.
 
+-  ``ERRATA_N2_2779511``: This applies errata 2779511 workaround to Neoverse-N2
+   CPU. This needs to be enabled for revisions r0p0, r0p1 and r0p2. It is fixed
+   in r0p3.
+
 For Cortex-X2, the following errata build flags are defined :
 
 -  ``ERRATA_X2_2002765``: This applies errata 2002765 workaround to Cortex-X2