errata: workaround for Neoverse V1 errata 2139242

Neoverse V1 erratum 2139242 is a Cat B erratum present in the V1
processor core.  This issue is present in revisions r0p0, r1p0,
and r1p1, and it is still open.

SDEN can be found here:
https://documentation-service.arm.com/static/60d499080320e92fa40b4625

Signed-off-by: John Powell <john.powell@arm.com>
Change-Id: I5c2e9beec72a64ac4131fb6dd76199821a934ebe
diff --git a/lib/cpus/cpu-ops.mk b/lib/cpus/cpu-ops.mk
index 4677f91..050a56e 100644
--- a/lib/cpus/cpu-ops.mk
+++ b/lib/cpus/cpu-ops.mk
@@ -397,6 +397,10 @@
 # exists in r0p0 as well but there is no workaround for that revision.
 ERRATA_V1_1966096   ?=0
 
+# Flag to apply erratum 2139242 workaround during reset. This erratum applies
+# to revisions r0p0, r1p0, and r1p1 of the Neoverse V1 cpu and is still open.
+ERRATA_V1_2139242   ?=0
+
 # Flag to apply DSU erratum 798953. This erratum applies to DSUs revision r0p0.
 # Applying the workaround results in higher DSU power consumption on idle.
 ERRATA_DSU_798953	?=0
@@ -726,6 +730,10 @@
 $(eval $(call assert_boolean,ERRATA_V1_1966096))
 $(eval $(call add_define,ERRATA_V1_1966096))
 
+# Process ERRATA_V1_2139242 flag
+$(eval $(call assert_boolean,ERRATA_V1_2139242))
+$(eval $(call add_define,ERRATA_V1_2139242))
+
 # Process ERRATA_DSU_798953 flag
 $(eval $(call assert_boolean,ERRATA_DSU_798953))
 $(eval $(call add_define,ERRATA_DSU_798953))