jtag: added method to retrieves number of devices in the JTAG chain

src/jtag.hpp

@@ -79,6 +79,12 @@ class Jtag {
 	 */
 	uint32_t get_target_device_id() {return _devices_list[device_index];}
 
+	/*!
+	 * \brief return JTAG chain length
+	 * \return number of devices present
+	 */
+	size_t get_chain_len() {return _devices_list.size();}
+
 	/*!
 	 * \brief set index for targeted FPGA
 	 * \param[in] index: index in the chain