sdl: add missing HINT_VIDEODRIVER hint

[gamelaster]

This hint is needed to force Wayland over X11.

Usage:

    sdl.SetHint(sdl.HINT_VIDEODRIVER, "wayland,x11")
    if err := sdl.Init(sdl.INIT_EVERYTHING); err != nil {
        panic(err)
    }
    defer sdl.Quit()

[veeableful]

Thank you @gamelaster!