fix(cpus): workaround for Cortex-A720 erratum 2844092

Cortex-A720 erratum 2844092 is a Cat B erratum that is present
in revisions r0p0, r0p1 and is fixed in r0p2.

The workaround is to set bit[11] of CPUACTLR4_EL1 register.

SDEN documentation:
https://developer.arm.com/documentation/SDEN-2439421/latest

Change-Id: I3d8eacb26cba42774f1f31c3aae2a0e6fecec614
Signed-off-by: Sona Mathew <sonarebecca.mathew@arm.com>
diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index f253cd3..7af2eae 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -932,6 +932,10 @@
 
 For Cortex-A720, the following errata build flags are defined :
 
+-  ``ERRATA_A720_2844092``: This applies errata 2844092 workaround to
+   Cortex-A720 CPU. This needs to be enabled for revisions r0p0 and r0p1.
+   It is fixed in r0p2.
+
 -  ``ERRATA_A720_2926083``: This applies errata 2926083 workaround to
    Cortex-A720 CPU. This needs to be enabled for revisions r0p0 and r0p1.
    It is fixed in r0p2.