Indicate this uses dlmalloc.

(cherry picked from commit d248c1ac846bd47fa776441e2b9c121ad1fe1919)

Change-Id: Id8fafa0dcef0a8c6c9705a9096d49b3423245944
diff --git a/BoardConfig.mk b/BoardConfig.mk
index 7c3007b..48bc59d 100644
--- a/BoardConfig.mk
+++ b/BoardConfig.mk
@@ -40,3 +40,4 @@
 
 TARGET_RECOVERY_FSTAB = device/asus/grouper/fstab.grouper
 
+MALLOC_IMPL := dlmalloc