Add support for NVIDIA Jetson / Jetson Nano

[baud_]

For the C-code examples provided by e-Paper, the build command for the NVidia JETSON is make JETSON. So for example, the Jetson target for the 4.2in B/W display would be make EPD=_4in2 JETSON.

I have the epd command working on the Jetson with a 4.2in ePaper display connected directly to the 40-pin header. Instructions for this setup are provided by e-Paper at the following links:

https://www.waveshare.com/wiki/Template:Jetson_Nano_Guides_for_SPI_e-Paper

https://www.waveshare.com/wiki/4.2inch_e-Paper_Module_Manual#User_Guides_of_Jetson_Nano