fix(cpus): workaround for Cortex-A520 erratum 2858100

Cortex-A520 erratum 2858100 is a Cat B erratum that applies to
all revisions <=r0p1 and is still open. The workaround is to
set bit[29] of CPUACTLR_EL1.

SDEN Documentation:
https://developer.arm.com/documentation/SDEN-2444153/latest

Signed-off-by: Arvind Ram Prakash <arvind.ramprakash@arm.com>
Change-Id: I5a07163f919352583b03328abd5659bf7b268677
diff --git a/include/lib/cpus/aarch64/cortex_a520.h b/include/lib/cpus/aarch64/cortex_a520.h
index 1c5f886..619a15d 100644
--- a/include/lib/cpus/aarch64/cortex_a520.h
+++ b/include/lib/cpus/aarch64/cortex_a520.h
@@ -12,6 +12,8 @@
 /*******************************************************************************
  * CPU Extended Control register specific definitions
  ******************************************************************************/
+#define CORTEX_A520_CPUACTLR_EL1				S3_0_C15_C1_0
+
 #define CORTEX_A520_CPUECTLR_EL1				S3_0_C15_C1_4
 
 /*******************************************************************************