Add workaround for ARM Cortex-A53 erratum 855873

ARM erratum 855873 applies to all Cortex-A53 CPUs.
The recommended workaround is to promote "data cache clean"
instructions to "data cache clean and invalidate" instructions.
For core revisions of r0p3 and later this can be done by setting a bit
in the CPUACTLR_EL1 register, so that hardware takes care of the promotion.
As CPUACTLR_EL1 is both IMPLEMENTATION DEFINED and can be trapped to EL3,
we set the bit in firmware.
Also we dump this register upon crashing to provide more debug
information.

Enable the workaround for the Juno boards.

Change-Id: I3840114291958a406574ab6c49b01a9d9847fec8
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/lib/cpus/cpu-ops.mk b/lib/cpus/cpu-ops.mk
index 7d7db20..132ab6f 100644
--- a/lib/cpus/cpu-ops.mk
+++ b/lib/cpus/cpu-ops.mk
@@ -66,6 +66,12 @@
 # erratum workaround is enabled by default in hardware.
 ERRATA_A53_836870	?=0
 
+# Flag to apply errata 855873 during reset. This errata applies to all
+# revisions of the Cortex A53 CPU, but this firmware workaround only works
+# for revisions r0p3 and higher. Earlier revisions are taken care
+# of by the rich OS.
+ERRATA_A53_855873	?=0
+
 # Flag to apply erratum 806969 workaround during reset. This erratum applies
 # only to revision r0p0 of the Cortex A57 cpu.
 ERRATA_A57_806969	?=0
@@ -106,6 +112,10 @@
 $(eval $(call assert_boolean,ERRATA_A53_836870))
 $(eval $(call add_define,ERRATA_A53_836870))
 
+# Process ERRATA_A53_855873 flag
+$(eval $(call assert_boolean,ERRATA_A53_855873))
+$(eval $(call add_define,ERRATA_A53_855873))
+
 # Process ERRATA_A57_806969 flag
 $(eval $(call assert_boolean,ERRATA_A57_806969))
 $(eval $(call add_define,ERRATA_A57_806969))