The standard u-boot as supplied on the linux-images and with build instructions here:
http://odroid.com/dokuwiki/doku.php?id=en:c2_building_u-boot
just works out of the box. Interrupt the standard boot process by hitting "Enter" twice and enter:
###For booting with TFTP
setenv serverip A.B.C.D (The address of your (FreeBSD) TFTP server)
setenv ipaddr D.E.F.G (The address of your C2)
setenv bootcmd "tftp 0x20000000 kernel; go 0x20001000"
saveenv
and on the next reboot (just enter "reset") it will boot with TFTP.
Just place the "kernel" file in your TFTP-server directory.
###For booting from SD
setenv bootcmd "fatload mmc 0:2 0x20000000 kernel; go 0x20001000"