machine 'fsref':
1. prepare sd card for booting, partition schema:
	1) primary partition for boot
		format: fat32
		  size: 2G
		 label: sdboot
	2) primary partition for rootfs
		format: ext4
		  size: remain
		 label: sdroot
2. copy boot files to sd card:
	1) sdboot part:
		1) boot.bin
			fsbl name is fixed determined by zynq,
			will be loaded into OCM,
			size limit is 192kb
		2) uImage
			Linux kernel
			name is determined by:
				include/configs/zynq-common.h: CONFIG_SPL_FS_LOAD_KERNEL_NAME
		3) system.dtb
			Linux device tree
			name is determined by:
				include/configs/zynq-common.h: CONFIG_SPL_FS_LOAD_ARGS_NAME
		4) fpga bit file
			e.g. FPGA_TOP_0505_02.bit
	2) sdroot part:
		mkdir <mount_dir>
		sudo mount /dev/mmcblk0p2 <mount_dir>
		cd <mount_dir>
		sudo tar -xf <xxx>/rootfs.tar.gz <mount_dir>
3. load fpga
	1) boot with sd card made in last step.
	1) prepare fpga bit file
		prepare_fpga <src_file_name> <dst_file_name>

		src_file_name: relative file name, located in /dev/mmcblk0p1
		dst_file_name: will be put in /lib/firmware
	2) load fpga file
		echo <dst_file_name> > /sys/class/fpga_manager/fpga0/firmware