Initial step of paging now just prepares fast page for heap, actual page
table initialization happens after heap is initialized which allows
x86_64 to never depend on kmalloc for pages.
Processor's stacks are now also spawned with PMM/VMM allocated stacks
instead of kmalloc identity mapped.
Also add custom load addresses for x86_64 target. This allows qemu to
load the kernel with -kernel argument. Without these addresses qemu
would refuse to load as it only supports 32 bit ELFs, but as our kernel
starts in 32 bit mode anyway, we can just load it!
This cleans up the kernel executable as bootloaders don't have to
load AP init code straight to 0xF000, but it will be moved there once
kernel is doing the AP initialization.
