[U-Boot] Workaround for SPL modifying the DTB before use

[Bartlomiej]

Hello,

We're implementing secure boot using HAB for an i.MX8M based board using 
U-Boot, specifically the fork from the `u-boot-imx6` repository from 
Boundary Devices. The reason i'm posting this here, is because the 
problematic behaviour we encountered seems to come from the mainline.

We have a FIT image which contains the U-Boot, ATF & the DTB. The SPL 
manipulates the DTB when booting the board by adding a memreserve 
section and an additional node into the FDT. This makes secure boot fail 
when verifying the DTB from the image, since it has a different length 
and contents. The workaround we used is removing the DTB from the 
U-Boot's FIT image and embedding it directly in the binary. This seems 
to work, but are there any better ways of fixing the above problem?

Best regards,
Bartlomiej Nowak