Add the du command to toolbox

The code is from NetBSD, with the -n and -h options removed to make
porting easy.  Also, removed support for the BLOCKSIZE environment
variable for the same reason.

Change-Id: Ib927ff3527e02802785fdd7f75bab1f05222918e
diff --git a/toolbox/Android.mk b/toolbox/Android.mk
index be95e7c..c1f165c 100644
--- a/toolbox/Android.mk
+++ b/toolbox/Android.mk
@@ -56,6 +56,7 @@
 	ionice \
 	touch \
 	lsof \
+        du \
 	md5
 
 ifeq ($(HAVE_SELINUX),true)