Building Uboot from make uboot command

I was going through the soc fpga training where it details building preloader, uboot etc . while building the preloader was straight forward, for building uboot, i used the command make uboot and it generated the uboot.img file which is what is necessary for uboot bringup on the hardware. but on rocketboards, i see we need to use yocto or angstrom to generate uboot files. this is for qspi boot, though it is the same for sdmmc as well. I wanted to know if these are different methods to build the uboot file or we should use the files generated by yocto project for uboot.

. would greatly appreciate any inputs.