bootable: Change how blank screen works

This is required on some devices where previous to 8.1/8.0 the blank
screen flag worked but don't now.

Test: Tested on begonia, screen is now no longer black

Change-Id: Ib4ff607d220bcb1aa5166fea23cc7ecb0e012fdd
(cherry picked from commit 28d8dec40d60a31309fcf6259dad38cd328f0717)
diff --git a/gui/Android.mk b/gui/Android.mk
index 33e870f..d9cae7f 100755
--- a/gui/Android.mk
+++ b/gui/Android.mk
@@ -119,6 +119,9 @@
 ifeq ($(AB_OTA_UPDATER),true)
     LOCAL_CFLAGS += -DAB_OTA_UPDATER=1
 endif
+ifeq ($(TW_SCREEN_BLANK_ON_BOOT), true)
+    LOCAL_CFLAGS += -DTW_SCREEN_BLANK_ON_BOOT
+endif
 
 LOCAL_C_INCLUDES += \
     bionic \