add private data pointer to the tap interface

This will give us the ability to add special data structures and new
interfaces without rewriting the complete jtag engine.

Change-Id: I21a6e1daa96c5f4d111bbb734c7c1fbc2eaee227
Signed-off-by: Mathias K <kesmtp@freenet.de>
Reviewed-on: http://openocd.zylin.com/244
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>

src/jtag/jtag.h

@@ -156,7 +156,9 @@ struct jtag_tap {
 
 	struct jtag_tap* next_tap;
 	/* dap instance if some null if no instance , initialized to 0 by calloc*/
-	struct adiv5_dap *dap; 
+	struct adiv5_dap *dap;
+	/* private pointer to support none-jtag specific functions */
+	void *priv;
 };
 
 void jtag_tap_init(struct jtag_tap *tap);