fix(cpus): workaround for Cortex-A78C erratum 1827440

Cortex-A78C erratum 1827440 is a Cat B erratum that applies to
revision r0p0 and is fixed in r0p1.

The workaround is to set CPUACTLR2_EL1[2], which forces atomic store
operations to write-back memory to be performed in the L1 data cache.

SDEN documentation:
https://developer.arm.com/documentation/SDEN1707916/latest

Signed-off-by: Bipin Ravi <bipin.ravi@arm.com>
Change-Id: I41d8ef48f70216ec66bf2b0f4f03ea8d8c261ee7
diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index 73c7ac5..0f1f92a 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -353,6 +353,10 @@
   Cortex-A78C CPU. This needs to be enabled for revision r0p0. The erratum is
   fixed in r0p1.
 
+- ``ERRATA_A78C_1827440`` : This applies errata 1827440 workaround to
+  Cortex-A78C CPU. This needs to be enabled for revision r0p0. The erratum is
+  fixed in r0p1.
+
 - ``ERRATA_A78C_2132064`` : This applies errata 2132064 workaround to
   Cortex-A78C CPU. This needs to be enabled for revisions r0p1, r0p2 and
   it is still open.