hikey/hikey960: Add ro.hardware.egl=mali

A recent AOSP/main change has put a hard dependency on
ro.hardware.egl or equivalent property being set, otherwise
it fails to boot successfully:

F DEBUG   : Cmdline: /system/bin/surfaceflinger
F DEBUG   : pid: 672, tid: 677, name: surfaceflinger  >>> /system/bin/surfaceflinger <<<
F DEBUG   : uid: 1000
F DEBUG   : tagged_addr_ctrl: 0000000000000001 (PR_TAGGED_ADDR_ENABLE)
F DEBUG   : signal 6 (SIGABRT), code -1 (SI_QUEUE), fault addr --------
F DEBUG   : Abort message: 'couldn't find an OpenGL ES implementation, make sure one of persist.graphics.egl, ro.hardware.egl and ro.board.platform is set'

Change-Id: Ifa82dd3ea480f88b3c2646c6ca40a99d9ef52849
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
diff --git a/hikey960.mk b/hikey960.mk
index 342fa04..dd7082b 100644
--- a/hikey960.mk
+++ b/hikey960.mk
@@ -52,7 +52,9 @@
 $(call inherit-product, device/linaro/hikey/device-common.mk)
 $(call inherit-product-if-exists, vendor/linaro/hikey960/$(EXPECTED_LINARO_VENDOR_VERSION)/hikey960.mk)
 
-PRODUCT_PROPERTY_OVERRIDES += ro.opengles.version=196608
+PRODUCT_PROPERTY_OVERRIDES += \
+  ro.opengles.version=196608 \
+  ro.hardware.egl=mali
 
 #
 # Overrides