Port semi-hosting bootwrapper to ARMv8

Currently the ARMv8 bootwrapper embeds kernel, device tree file, kernel command line and optional initrd into a single axf file. Since Foundation model needs a different device tree file than RTSM model, this means we need to build and ship to axf files. This also means developers cannot easily boot their own kernels, as they have to rebuild wrapper with their new ke
rnel as an extra step.

For ARMv7 we have a semihosting bootwrapper, which loads the boot artifacts from separate files, meaning one can use the same semihosting wrapper for all uses. Add support for ARMv8 to this codebase so we can boot ARMv8 models in the same way.