Add the sdk overlay to the build.

Change-Id: I4d3d08a13d23194a84fdd822a130f9aa71bb6360
diff --git a/target/product/sdk.mk b/target/product/sdk.mk
index ba105f8..572b823 100644
--- a/target/product/sdk.mk
+++ b/target/product/sdk.mk
@@ -30,6 +30,8 @@
 	GestureBuilder \
 	SoftKeyboard
 
+PRODUCT_PACKAGE_OVERLAYS := development/sdk_overlay
+
 PRODUCT_COPY_FILES := \
 	development/data/etc/vold.conf:system/etc/vold.conf \
 	frameworks/base/data/etc/android.hardware.camera.autofocus.xml:system/etc/permissions/android.hardware.camera.autofocus.xml