Add 'blank_screen' to embedded.mk.

This utility shuts off the screen.

Bug: 70846424
Test: manual + w/ init
Change-Id: I11bf8b709e81dd127de7d12c50da4ab5be456cfb
diff --git a/target/product/embedded.mk b/target/product/embedded.mk
index 20f0ebf..6e6d5b5 100644
--- a/target/product/embedded.mk
+++ b/target/product/embedded.mk
@@ -25,6 +25,7 @@
     android.hidl.memory@1.0-impl \
     android.hidl.memory@1.0-impl.vendor \
     atrace \
+    blank_screen \
     bootanimation \
     bootstat \
     charger \