Fix home target

Have a no-op home target if there's no home partition

Test: m docker-home with Excelsior
Change-Id: Ida2da14b6a71f63518c3c3590818610a329d41b9
diff --git a/home.mk b/home.mk
index c2af8ca..fcb57f7 100644
--- a/home.mk
+++ b/home.mk
@@ -22,6 +22,7 @@
 HOME_DIR := $(PRODUCT_OUT)/obj/HOME
 HOME_RAW_IMG := $(PRODUCT_OUT)/obj/HOME/home.raw.img
 HOME_IMG := $(PRODUCT_OUT)/home.img
+endif
 
 $(HOME_DIR):
 	mkdir -p $(HOME_DIR)
@@ -33,13 +34,17 @@
 
 $(HOME_RAW_IMG): $(HOME_DIR)
 	$(LOG) home raw-build
-	fallocate -l $(HOME_SIZE_MB)M $(HOME_RAW_IMG)
-	mkfs.ext4 -F -j $(HOME_RAW_IMG)
+	ifneq ($(HOME_SIZE_MB),)
+		fallocate -l $(HOME_SIZE_MB)M $(HOME_RAW_IMG)
+		mkfs.ext4 -F -j $(HOME_RAW_IMG)
+	endif
 	$(LOG) home raw-build finished
 
 $(HOME_IMG): $(HOST_OUT)/bin/img2simg $(HOME_RAW_IMG)
 	$(LOG) home img2simg
-	$(HOST_OUT)/bin/img2simg $(HOME_RAW_IMG) $(HOME_IMG)
+	ifneq ($(HOME_SIZE_MB),)
+		$(HOST_OUT)/bin/img2simg $(HOME_RAW_IMG) $(HOME_IMG)
+	endif
 	$(LOG) rootfs img2simg finished
 
 clean::
@@ -49,4 +54,3 @@
 	@echo "home - creates the home partition image"
 
 .PHONY:: home home_raw
-endif