Indicate this uses dlmalloc.

(cherry picked from commit c5258394a2a448fedcf80a45b0111b9667f8a4fe)

Change-Id: Ida9b67d4418d647046d2174d872109114e772083
diff --git a/BoardConfig.mk b/BoardConfig.mk
index d1b87d9..1e331cd 100644
--- a/BoardConfig.mk
+++ b/BoardConfig.mk
@@ -41,3 +41,5 @@
 include device/asus/grouper/BoardConfigCommon.mk
 
 TARGET_RECOVERY_FSTAB = device/asus/tilapia/fstab.grouper
+
+MALLOC_IMPL := dlmalloc