x86_64: clear exactly 3 pages to avoid multiboot overwrite
x86_64: clear exactly 3 pages to avoid multiboot overwrite

alfred-bratterud/IncludeOS,mnordsletten/IncludeOS,mnordsletten/IncludeOS,ingve/IncludeOS,AnnikaH/IncludeOS,ingve/IncludeOS,mnordsletten/IncludeOS,AnnikaH/IncludeOS,AndreasAakesson/IncludeOS,alfred-bratterud/IncludeOS,AnnikaH/IncludeOS,alfred-bratterud/IncludeOS,ingve/IncludeOS,ingve/IncludeOS,mnordsletten/IncludeOS,AndreasAakesson/IncludeOS,ingve/IncludeOS,alfred-bratterud/IncludeOS,AndreasAakesson/IncludeOS,AndreasAakesson/IncludeOS,hioa-cs/IncludeOS,mnordsletten/IncludeOS,AnnikaH/IncludeOS,AndreasAakesson/IncludeOS,hioa-cs/IncludeOS,hioa-cs/IncludeOS,AndreasAakesson/IncludeOS,AnnikaH/IncludeOS,hioa-cs/IncludeOS,alfred-bratterud/IncludeOS,hioa-cs/IncludeOS,mnordsletten/IncludeOS