fix(cpus): workaround for Cortex-A78C erratum 2772121

Cortex-A78C erratum 2772121 is a Cat B erratum that applies to
all revisions <=r0p2 and is still open. The workaround is to
insert a dsb before the isb in the power down sequence.

SDEN documentation:
https://developer.arm.com/documentation/SDEN1707916/latest

Signed-off-by: Bipin Ravi <bipin.ravi@arm.com>
Change-Id: I0e190dabffc20c4d3b9b98d1abeb50f308b80bb9
diff --git a/lib/cpus/cpu-ops.mk b/lib/cpus/cpu-ops.mk
index c9b4447..a1126fa 100644
--- a/lib/cpus/cpu-ops.mk
+++ b/lib/cpus/cpu-ops.mk
@@ -394,6 +394,10 @@
 # to revisions r0p1 and r0p2 of the A78C cpu. It is still open.
 ERRATA_A78C_2395411 	?=0
 
+# Flag to apply erratum 2772121 workaround during powerdown. This erratum
+# applies to revisions r0p0, r0p1 and r0p2 of the A78C cpu. It is still open.
+ERRATA_A78C_2772121 	?=0
+
 # Flag to apply erratum 1821534 workaround during reset. This erratum applies
 # to revisions r0p0 - r1p0 of the X1 cpu and fixed in r1p1.
 ERRATA_X1_1821534	?=0
@@ -1062,6 +1066,10 @@
 $(eval $(call assert_boolean,ERRATA_A78C_2395411))
 $(eval $(call add_define,ERRATA_A78C_2395411))
 
+# Process ERRATA_A78C_2772121 flag
+$(eval $(call assert_boolean,ERRATA_A78C_2772121))
+$(eval $(call add_define,ERRATA_A78C_2772121))
+
 # Process ERRATA_X1_1821534 flag
 $(eval $(call assert_boolean,ERRATA_X1_1821534))
 $(eval $(call add_define,ERRATA_X1_1821534))