Co-authored-by: Victor Perevertkin <victor.perevertkin@reactos.org>
Introduce the initial changes needed to get other processors up and into kernel mode.
This only supports x86 as of now but is the first real step towards using other system processors.
Lazy IRQL feature has issues with interrupt delivery on VirtualBox, so disable it for now.
For the feature description, see commit d28eae967a
Meanwhile, merge and clean up APIC headers a bit