valve-steamdeck: new device

A good portion of this was copypasta'd from the x64 eufi tablet "device" package, some may need to be further modified to improve things later.

Note that only the "linux-edge" kernel is used, and it's likely that this kernel is still missing some functionality. I'd like to avoid using a downstream/forked kernel if at all possible...

Also the way that the cmdline options are in a grub.cfg is... really ugly... Yes, I know :P