gfxboot is now loaded via a COM module. If you used a line like

gfxboot bootlogo

before in isolinux.cfg or syslinux.cfg, change this to

ui gfxboot.com bootlogo

and add /usr/share/syslinux/gfxboot.com to your boot directory (the one
where the config file is).

This also means that gfxboot now works with other syslinux variants like
pxelinux or extlinux, too.