uboot实现了传递dtb的功能，#define CONFIG_OF_LIBFDT使能设备树

i.mx6ul实现方式：

#if defined(CONFIG_SYS_BOOT_NAND)
#define CONFIG_EXTRA_ENV_SETTINGS \
        CONFIG_MFG_ENV_SETTINGS \
        "panel=TFT43AB\0" \
        "fdt_addr=0x83000000\0" \
        "fdt_high=0xffffffff\0"   \
        "console=ttymxc0\0" \
        "bootargs=console=ttymxc0,115200 "  \
                "root=ubi0:rootfs rootfstype=ubifs "                 \
                "ubi.mtd=5 mtdparts=gpmi-nand:4m(u-boot),2m(u-boot-env),4m(logo),10m(kernel),2m(dtb),-(rootfs) rootwait rw\0"\
        "bootcmd=nand read ${loadaddr} 0xa00000 0xa00000;"\
                "nand read ${fdt_addr} 0x1400000 0x200000;"\
                "bootz ${loadaddr} - ${fdt_addr}\0"
#else
（1）将kernel载入内存

nand read ${loadaddr} 0xa00000 0xa00000

（2）然后用fdt addr ${fdtaddr}命令将dtb载入内存

nand read ${fdt_addr} 0x1400000 0x200000

（3）使用bootz ${loadaddr} ${initrdaddr} ${fdtaddr}来引导内核

initrd是临时文件系统，实际使用时用“-”代替：bootz ${loadaddr} - ${fdtaddr}

bootz ${loadaddr} - ${fdt_addr}