Controlled by the embedder defining CFG_TUD_FSDEV_DOUBLE_BUFFERED_ISO_EP
in tusb_config.h. If hardware does have SBUF_ISO bit it will use only
one half of endpoint pair register.
- skip DIR and use CTR TX/RX to handle complete transfer
- clear CTR first, except for setup which we need to get data first
- separate handle_ctr_setup()
