adding device custom class support

add usbd_open_edpt_pair

tinyusb/device/usbd_pvt.h

@@ -50,6 +50,9 @@ extern osal_semaphore_t _usbd_ctrl_sem;
 tusb_error_t usbd_init(void);
 void         usbd_task( void* param);
 
+// helper to parse an pair of In and Out endpoint descriptors. They must be consecutive
+tusb_error_t usbd_open_edpt_pair(uint8_t rhport, tusb_desc_endpoint_t const* p_desc_ep, uint8_t xfer_type, uint8_t* ep_out, uint8_t* ep_in);
+
 // Carry out Data and Status stage of control transfer
 //tusb_error_t usbd_control_xfer_st(uint8_t rhport, tusb_dir_t dir, uint8_t * buffer, uint16_t length);