configure --enable-gst to turn on gst plugin build

 default: configure would disable gstreamer plugin build

Signed-off-by: Wind Yuan <feng.yuan@intel.com>
diff --git a/wrapper/Makefile.am b/wrapper/Makefile.am
index 875ebce..63dbffd 100644
--- a/wrapper/Makefile.am
+++ b/wrapper/Makefile.am
@@ -1 +1,8 @@
-SUBDIRS = gstreamer
+
+if ENABLE_GST
+GST_DIR = gstreamer
+else
+GST_DIR =
+endif
+
+SUBDIRS = $(GST_DIR)