add cdc_serial_app for virtual com demo
add api for usbh: tusbh_device_get_mounted_class_flag implement api for custom class - is mounted - read
refractor usbh class driver indexing opt out periodic list code in EHCI (need to refractor/group later) [device lpc176x] rename dcd_endpoint_configure to dcd_pipe_open add usbd_pipe_open to manage pipe