Indicate this uses dlmalloc.

(cherry picked from commit 744b4d58552f57b82dff15c8d7bd30599b6b4604)

Change-Id: I0452888e34ae1a6daf3a0579ae610fa27c022dbf
diff --git a/BoardConfig.mk b/BoardConfig.mk
index 9f79b96..767f08b 100755
--- a/BoardConfig.mk
+++ b/BoardConfig.mk
@@ -93,3 +93,5 @@
 	file.te \
 	mediaserver.te \
 	system_server.te
+
+MALLOC_IMPL := dlmalloc