Hello Kanimozhi Thangappan,
I do not have experience with Mender so I do not know how it may affect Yocto’s behavior, if it does.
As for the .imx bootloader file, it is generated by the imx-mkimage package, specifically the imx-boot recipe which is called bu the u-boot-imx recipe. Are you using u-boot-imx to generate the bootloader? This should be the preferred u-boot for the imx6ulevk MACHINE but I checked the imx6ulevk.conf file and it’s not specified so maybe just adding it may do the trick.
Ty opening the imx6ulevk configuration file:
imx-yocto-bsp/sources/meta-fsl-bsp-release/imx/meta-bsp/conf/machine/imx6ulevk.conf
And adding:
PREFERRED_PROVIDER_u-boot = "u-boot-imx"
And then bake the bootloader or image again.
I hope this helps!
Regards,