Recent version of U-Boot v2022.01 reverted boot container generation
mechanism to provide single boot container isntead of separate binaries
for SPL+DDR and U-Boot FIT. New approach provides packing of those
separate components inside the U-Boot binman, and is delivered as a
single 'flash.bin' file, which resembles the original behavior before
binman image packing was introduced.
Adapt our boot container class and WIC file to pick up this consolidated
binary instead of two separate pieces.
