Add display-driver + GUD example

[rhgndf]

These kinds of examples would be interesting to add: Use the Linux GUD driver to make the microcontroller act as an additional display output and let your desktop be joined to the screen. This will need a GUD class driver to be added to embassy.

I'm using this as an easy way to try to display images and test out brightness levels on the displays

[decaday]

This is so awesome!

However, this PR just needs a rebase onto master and an update to Cargo.toml .

I don't have a CH32V305, so I ported it to the RP2040 instead. It ran successfully in the end, verifying that the code itself should be fine.

However, it looks like the VID:PID (1209:4FB3) used by the embassy-usb GUD class was only added to the Linux kernel in this patch. I am using kernel 7.1.3, and the first kernel version to include this patch is 7.2, so I spent some time troubleshooting this issue. Perhaps a quick note could be added to the example comments to remind users.

[rhgndf]

This is so awesome!

Thanks!

This will work much better with usb2/usb3 and a larger screen. ch32v305 has high-speed usb, so I got close to 60fps out of it.

I have also submitted a patch to make the default vid/pid the first one which should be supported since the driver has been introduced in the linux kernel.

I think you might have to wait until a new embassy-usb is released before merging this, since the gud class driver is still in the unreleased part.