usage mmc card as fs partition and boot disk

We have never try/implement this before. However if you want to try here are some points. First check in HRM if you DSP processor support MMC boot. Then do some study to boot the u-boot from MMC, if lucky enough you get the u-boot boot sucessfully from MMC card and get the first block  saying 512B on the MMC card free for storing the MBR information for your SD partitioning. Then you use utilites like fdisk to make partition on your MMC and you make filesystems on it to storting data.  So the totoal layout would be like this: first 512B for MBR, comming un-patitioned region to store u-boot and kernel image, followd by the partitioned regions to store your root filesystem and user data.

I just checked the HRM and EZKIT user maual for Processors like BF537, BF548 and BF518 looks like they does not support from MMC card, so you will have to store your bootloader in some other storage like a SPI Flash, for other part like the kernel, rootfs and user data you may store it in the MMC