STM32 ACM Linux 驱动添加

• kernel 内驱动添加如下：

    x Symbol: USB_ACM [=y]                                                    x
    x Type  : tristate                                                        x
    x Prompt: USB Modem (CDC ACM) support                                     x
    x   Defined at drivers/usb/class/Kconfig:7                                x
    x   Depends on: USB_SUPPORT [=y] && USB [=y]                              x
    x   Location:                                                             x
    x     -> Device Drivers                                                   x
    x       -> USB support (USB_SUPPORT [=y])                                 x
    x   Selected by: USB_VL600 [=n] && NETDEVICES [=y] && USB [=y] && NET [=y 

• 添加后单片机可变为 ttyUSB 设备