Hello Liviu,
For imx7ul-evk, fdt_file name is defined in u-boot/include/configs/mx7ulp_evk.h, see below, please!
......
"fdt_file=" CONFIG_DEFAULT_FDT_FILE ".dtb\0" \
......
Actuall, she can modify it like this:
#define MY_DTB_FILE "mx7ulp_customized"
......
"fdt_file=" MY_DTB_FILE ".dtb\0" \
......
or
......
"fdt_file=" mx7ulp_customized ".dtb\0" \
......
Then run : bitbake -f -c compile u-boot-imx or bitbake u-boot-imx -c compile -f
So don't need to make a special path for the change.
Hope above information is helpful for you.
Have a nice day!
B.R,
Weidong