Unlike older i.MX processor you don't need to select CONFIG_SKIP_LOWLEVEL_INIT because U-Boot lowlevel for i.MX51 doesn't reconfigure RAM memory. It is configured on DCD table.
Copy u-boot.bin to /tftpboot because BDI3000 will load it from there.
Connect the serial console cable on your i.MX51EVK board and connect to it using minicom.
Connect to your BDI3000 through telnet and execute these commands:
FSL-iMX51> load 0x97800000 u-boot.binLoading u-boot.bin , please wait ....Loading program file passedFSL-iMX51> rm pc 0x97800000FSL-iMX51> go
FSL-iMX51> load 0x97800000 u-boot.bin
Loading u-boot.bin , please wait ....
Loading program file passed
FSL-iMX51> rm pc 0x97800000
When you execute the last command (“go”) you will see U-Boot starting on serial console.