improve host configuration parsing

- remove driver class code binding
- fully support IAD
- auto calculate total length for interface descriptor for driver

src/host/usbh_classdriver.h

@@ -43,8 +43,6 @@ typedef struct {
   char const* name;
   #endif
 
-  uint8_t class_code;
-
   void     (* const init       )(void);
   uint16_t (* const open       )(uint8_t rhport, uint8_t dev_addr, tusb_desc_interface_t const * itf_desc, uint16_t max_len);
   bool     (* const set_config )(uint8_t dev_addr, uint8_t itf_num);