Please configure U-boot for SD boot.
For example (under U-boot):
setenv bootargs_mmc 'setenv bootargs ${bootargs} root=/dev/mmcblk0p1 ip=none rootfstype=ext2'
setenv bootcmd_mmc 'run bootargs_base bootargs_mmc;mmcinit;cp.b 0x100000 ${loadaddr} 0x200000;bootm ${loadaddr}'
setenv bootcmd 'run bootcmd_mmc'
saveenv