Kernel/x86: Bake the Prekernel and the Kernel into one image

[supercomputer7]

The new baked image is a Prekernel and a Kernel baked together now, so essentially we no longer need to pass the Prekernel as -kernel and the actual kernel image as -initrd to QEMU, leaving the option to pass an actual initrd or initramfs module later on with multiboot.

This tries to revive the work from #18027 after it was reverted in #18556. I tried to change things the least I could this time (also, I don't try to iterate on the modules' array anymore, and only pass the physical address and bytes count of the first module to the kernel so it can reserve that range for now).

cc @timschumi @ADKaster

[timschumi]

Boots fine now on my system (which had issues with the previous revision of the patch). This was already massaged once before (and therefore still looks fine now), so I only have some small things to point out.

[supercomputer7]

Boots fine now on my system (which had issues with the previous revision of the patch). This was already massaged once before (and therefore still looks fine now), so I only have some small things to point out.

I suspect the crashing in the previous iteration was happening because I aligned the physical address according to the mapping base of the kernel and it was incorrect? I don't really know, but this should work OK.

Anyway, I sent a fix to resolve what you asked to change, so if it passes CI, it should be good to go :)

[supercomputer7]

When merged, this should close #18558.

[timschumi]

Seems to work fine, let's reland this.