add working usb cdc with 48MHz clock

...ded/usb-adafruit-cdc/usb-adafruit-cdc/board_definitions.h

...d/usb-adafruit-cdc/usb-adafruit-cdc/board_driver_serial.c

...d/usb-adafruit-cdc/usb-adafruit-cdc/board_driver_serial.h

...dded/usb-adafruit-cdc/usb-adafruit-cdc/board_driver_usb.c

...dded/usb-adafruit-cdc/usb-adafruit-cdc/board_driver_usb.h

embedded/usb-adafruit-cdc/usb-adafruit-cdc/board_init.c

embedded/usb-adafruit-cdc/usb-adafruit-cdc/main.c

embedded/usb-adafruit-cdc/usb-adafruit-cdc/sam_ba_cdc.c

embedded/usb-adafruit-cdc/usb-adafruit-cdc/sam_ba_cdc.h

embedded/usb-adafruit-cdc/usb-adafruit-cdc/sam_ba_monitor.c

embedded/usb-adafruit-cdc/usb-adafruit-cdc/sam_ba_monitor.h

embedded/usb-adafruit-cdc/usb-adafruit-cdc/sam_ba_serial.c

embedded/usb-adafruit-cdc/usb-adafruit-cdc/sam_ba_serial.h

embedded/usb-adafruit-cdc/usb-adafruit-cdc/sam_ba_usb.c

embedded/usb-adafruit-cdc/usb-adafruit-cdc/sam_ba_usb.h