sdl: Make Palette and PixelFormat a struct
sdl: Make Palette and PixelFormat a struct

https://bugzilla.gnome.org/show_bug.cgi?id=778052

GNOME/vala,frida/vala,frida/vala,frida/vala,frida/vala,GNOME/vala,GNOME/vala,frida/vala,GNOME/vala