fix(cpus): workaround for Cortex-A78 erratum 2779479

Cortex-A78 erratum 2779479 is a Cat B erratum that applies to
all revisions <= r1p2 and is still open.

The workaround is to set the CPUACTLR3_EL1[47] bit to 1. Setting this
bit might have a small impact on power and negligible impact
on performance.

SDEN documentation:
https://developer.arm.com/documentation/SDEN1401784/latest

Change-Id: I3779fd1eff3017c5961ffa101b357918070b3b36
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 8a8445d..4ae4e54 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -321,6 +321,10 @@
    CPU. This needs to be enabled for revisions r0p0, r1p0, r1p1, and r1p2, and
    it is still open.
 
+-  ``ERRATA_A78_2779479``: This applies erratum 2779479 workaround to Cortex-A78
+   CPU. This needs to be enabled for revisions r0p0, r1p0, r1p1 and r1p2 and
+   it is still open.
+
 For Cortex-A78 AE, the following errata build flags are defined :
 
 - ``ERRATA_A78_AE_1941500`` : This applies errata 1941500 workaround to