Add Xbox One Elite and Xbox 360 Afterglow pads (Linux)

I noticed two of my favorite gamepads were unknown and didn't fit the fallback map, so I generated SDL2 map strings for them using this tool and have been using them locally - no additional mapping work was necessary as Xinput already had correct mappings for both devices out of the box. I also verified that the Steam Big Picture configuration resolves the same mappings for these two controllers.

For naming the devices, I web searched their GUIDs and tried to use the most common names that others are using for them in the wild.