Move to gpio character device implementation

[pjueon]

• related to: NVIDIA/jetson-gpio#81
• Nvidia's official Jetson.GPIO's implementation has been changed to use gpio character device, instead of sysfs.
• JetsonGPIO should be changed to gpio character device implementation too, so that it can easily grab updates and features from the official Jetson.GPIO repository.

[pjueon]

Read:

• https://www.thegoodpenguin.co.uk/blog/stop-using-sys-class-gpio-its-deprecated/

• https://blog.lxsang.me/post/id/33