Add basic readlink command

Change-Id: I693c1098e6c6d107a9e97285bf826ab153a1c8f0
diff --git a/toolbox/Android.mk b/toolbox/Android.mk
index f60037d..75ce53f 100644
--- a/toolbox/Android.mk
+++ b/toolbox/Android.mk
@@ -68,7 +68,8 @@
 	load_policy \
 	swapon \
 	swapoff \
-	mkswap
+	mkswap \
+	readlink
 
 ifneq (,$(filter userdebug eng,$(TARGET_BUILD_VARIANT)))
 TOOLS += r