build: dt_image: use prebuilt lz4 binary for compressing

* Also remove the lz4c fallback. We're providing an lz4
  binary that works, so it shouldn't ever have to fall back
  to lz4c.

Change-Id: I31d1d8eb73ccb59e77012e1397b20b393b0c003f
diff --git a/build/tasks/dt_image.mk b/build/tasks/dt_image.mk
index 2e68bfb..d4c6054 100644
--- a/build/tasks/dt_image.mk
+++ b/build/tasks/dt_image.mk
@@ -42,7 +42,7 @@
 $(INSTALLED_DTIMAGE_TARGET): $(DTBTOOL) $(INSTALLED_KERNEL_TARGET)
 	$(build-dtimage-target)
 ifeq ($(strip $(BOARD_KERNEL_LZ4C_DT)),true)
-	lz4 -9 < $@ > $(LZ4_DT_IMAGE) || lz4c -c1 -y $@ $(LZ4_DT_IMAGE)
+	prebuilts/tools-bliss/${HOST_OS}-x86/bin/lz4 -9 < $@ > $(LZ4_DT_IMAGE)
 	$(hide) $(ACP) $(LZ4_DT_IMAGE) $@
 endif
 	@echo "Made DT image: $@"