errata: workaround for Cortex-A710 erratum 2083908

Cortex-A710 erratum 2083908 is a Cat B erratum that applies to
revision r2p0 and is still open. The workaround is to set
CPUACTLR5_EL1[13] to 1.

SDEN can be found here:
https://developer.arm.com/documentation/SDEN1775101/latest

Signed-off-by: nayanpatel-arm <nayankumar.patel@arm.com>
Change-Id: I876d26a7ac6ab0d7c567a9ec9f34fc0f952589d8
diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index bde6d97..80e7821 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -389,6 +389,10 @@
    Cortex-A710 CPU. This needs to be enabled for revisions r0p0, r1p0 and r2p0
    of the CPU and is still open.
 
+-  ``ERRATA_A710_2083908``: This applies errata 2083908 workaround to
+   Cortex-A710 CPU. This needs to be enabled for revision r2p0 of the CPU and
+   is still open.
+
 For Neoverse N2, the following errata build flags are defined :
 
 -  ``ERRATA_N2_2067956``: This applies errata 2067956 workaround to Neoverse-N2