fix(cpus): workaround for Cortex-X4 erratum 2923985

Cortex-X4 erratum 2923935 is a Cat B erratum that applies
to all revisions <= r0p1 and is fixed in r0p2.

The workaround is to set CPUACTLR4_EL1[11:10] to 0b11.

SDEN documentation:
https://developer.arm.com/documentation/SDEN-2432808/latest

Signed-off-by: Arvind Ram Prakash <arvind.ramprakash@arm.com>
Change-Id: I9207802ad479919a7f77c1271019fa2479e076ee
diff --git a/lib/cpus/cpu-ops.mk b/lib/cpus/cpu-ops.mk
index 4c20785..4a04a9d 100644
--- a/lib/cpus/cpu-ops.mk
+++ b/lib/cpus/cpu-ops.mk
@@ -843,6 +843,10 @@
 # to revisions r0p0 and r0p1 of the Cortex-X4 cpu. It is fixed in r0p2.
 CPU_FLAG_LIST += ERRATA_X4_2897503
 
+# Flag to apply erratum 2923985 workaround on reset. This erratum applies
+# to revisions r0p0 and r0p1 of the Cortex-X4 cpu. It is fixed in r0p2.
+CPU_FLAG_LIST += ERRATA_X4_2923985
+
 # Flag to apply erratum 3076789 workaround on reset. This erratum applies
 # to revisions r0p0 and r0p1 of the Cortex-X4 cpu. It is fixed in r0p2.
 CPU_FLAG_LIST += ERRATA_X4_3076789