[yocto] How to modify u-boot in Root File System rootfs.ext2.gz.u-boot ?

[Jack lemon]

Hi everybody,

I worked with P1022DS-PB and then designed my custom board according to its
documents. For sd card I adjust u-boot to 115200 baud rate and compile it
with ELDK independently. However in Nor-flash we haven't u-boot.bin
independently. For Nor-Flash I need to adjust baud rate in .ext2.gz.u-boot
image, because for Nor-Flash only kernel,rootfs,dtb files are needed.
How can I modify u-boot in fsl-image-minimal-p1022ds.ext2.gz.u-boot for
adjusting baud rate to 115200?