fix(errata): workaround for Cortex-A710 erratum 2147715

Cortex-A710 erratum 2147715 is a Cat B erratum that applies
to revision r2p0 of the CPU, and is fixed in r2p1. The work-
around is to set CPUACTLR_EL1[22]=1. Setting this will cause
the CFP instruction to invalidate all branch predictor resources
regardless of the context.

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

Signed-off-by: Akram Ahmad <Akram.Ahmad@arm.com>
Change-Id: I94771bc1fc9b65a0c17d75200ec2b1df8a3279c6
diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index e15c82e..e02cd1d 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -472,6 +472,10 @@
    Cortex-A710 CPU. This needs to be enabled for revisions r0p0, r1p0 and r2p0
    of the CPU and is fixed in r2p1.
 
+-  ``ERRATA_A710_2147715``: This applies errata 2147715 workaround to
+   Cortex-A710 CPU. This needs to be enabled for revision r2p0 of the CPU
+   and is fixed in r2p1.
+
 -  ``ERRATA_A710_2282622``: This applies errata 2282622 workaround to
    Cortex-A710 CPU. This needs to be enabled for revisions r0p0, r1p0 and r2p0
    of the CPU and is fixed in r2p1.