We have an ebuild for u-boot-tools but we need one for u-boot which would install MLO and u-boot.img to /boot.
an ebuild for u-boot itself doesn't really make sense. it's like having an ebuild for the kernel -- we could install the sources, but you'd still have to build it for your specific target. considering how many devices maintain their own vendor forks, i don't think we want to get into that mess.