flash/nor: implement flash bank deallocation on OpenOCD exit

Change-Id: I8fcf09b2a85b3b68743f5fd68a31edea933b9b17
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/4414
Tested-by: jenkins
Reviewed-by: Matthias Welwarsky <matthias@welwarsky.de>

src/flash/nor/driver.h

@@ -209,6 +209,14 @@ struct flash_driver {
 	 * @returns ERROR_OK if successful; otherwise, an error code.
 	 */
 	int (*auto_probe)(struct flash_bank *bank);
+
+	/**
+	 * Deallocates private driver structures.
+	 * Use default_flash_free_driver_priv() to simply free(bank->driver_priv)
+	 *
+	 * @param bank - the bank being destroyed
+	 */
+	void (*free_driver_priv)(struct flash_bank *bank);
 };
 
 #define FLASH_BANK_COMMAND_HANDLER(name) \