hikey960: enable options to fix errata

Fix cortex a53 errata issues: #836870, #843419, #855873.
Signed-off-by: Victor Chong <victor.chong@linaro.org>
Acked-by: Haojian Zhuang <haojian.zhuang@linaro.org>

plat/hisilicon/hikey960/platform.mk

@@ -63,3 +63,8 @@ BL31_SOURCES		+=	drivers/arm/cci/cci.c			\
 				plat/hisilicon/hikey960/drivers/pwrc/hisi_pwrc.c \
 				plat/hisilicon/hikey960/drivers/ipc/hisi_ipc.c \
 				${HIKEY960_GIC_SOURCES}
+
+# Enable workarounds for selected Cortex-A53 errata.
+ERRATA_A53_836870		:=	1
+ERRATA_A53_843419		:=	1
+ERRATA_A53_855873		:=	1