added usbd_edpt_xfer/usbd_edpt_busy to replace dcd_edpt_transfer/dcd_edpt_busy()

- improve fifo write/read_n with only one lock
- use usbd_edpt_xfer/usbd_edpt_busy for hid/cdc/msc class driver
- replace cdc read's pending_read_from_host by usbd_edpt_busy()

src/device/usbd_pvt.h

@@ -33,11 +33,12 @@
  extern "C" {
 #endif
 
-//--------------------------------------------------------------------+
-// INTERNAL API for stack management
-//--------------------------------------------------------------------+
 bool usbd_init (void);
 
+//--------------------------------------------------------------------+
+// USBD Endpoint API
+//--------------------------------------------------------------------+
+
 // Carry out Data and Status stage of control transfer
 // - If len = 0, it is equivalent to sending status only
 // - If len > wLength : it will be truncated
@@ -46,6 +47,12 @@ bool usbd_control_xfer(uint8_t rhport, tusb_control_request_t const * request, v
 // Send STATUS (zero length) packet
 bool usbd_control_status(uint8_t rhport, tusb_control_request_t const * request);
 
+// Submit a usb transfer
+bool usbd_edpt_xfer        (uint8_t rhport, uint8_t ep_addr, uint8_t * buffer, uint16_t total_bytes);
+
+// Check if endpoint transferring is complete
+bool usbd_edpt_busy        (uint8_t rhport, uint8_t ep_addr);
+
 void usbd_edpt_stall(uint8_t rhport, uint8_t ep_addr);
 void usbd_edpt_clear_stall(uint8_t rhport, uint8_t ep_addr);
 bool usbd_edpt_stalled(uint8_t rhport, uint8_t ep_addr);