fix(cpus): workaround for Cortex-A715 erratum 2420947

Cortex-A715 erratum 2420947 is a cat B erratum that applies only
to revision r1p0 and is fixed in r1p1. The workaround is to set
bit[33] of CPUACTLR2_EL1. This will prevent store and store-release
to merge inside the write buffer, and it is not expected to have
much performance impacts.

SDEN can be found here:
https://developer.arm.com/documentation/SDEN2148827/latest

Change-Id: I01a71b878cd958e742ff8357f8cdfbfc5625de47
Signed-off-by: Bipin Ravi <biprav01@u203721.austin.arm.com>
diff --git a/lib/cpus/cpu-ops.mk b/lib/cpus/cpu-ops.mk
index 5e68dda..5bdd9e4 100644
--- a/lib/cpus/cpu-ops.mk
+++ b/lib/cpus/cpu-ops.mk
@@ -911,6 +911,10 @@
 # This erratum applies to revisions r0p0, r0p1. Fixed in r0p2.
 CPU_FLAG_LIST += ERRATA_V2_2801372
 
+# Flag to apply erratum 2420947 workaround during reset. This erratum applies
+# only to revision r1p0. It is fixed in r1p1.
+CPU_FLAG_LIST += ERRATA_A715_2420947
+
 # Flag to apply erratum 2429384 workaround during reset. This erratum applies
 # to revision r1p0. There is no workaround for r0p0. It is fixed in r1p1.
 CPU_FLAG_LIST += ERRATA_A715_2429384