This is the final part of the major mm subsystem
refactor (for now). The new and improved slab
allocator can do *proper* poisoning, with pretty
accurate out-of-bounds and use-after-free
detection.
vm_page_t has also been restructured; its flags
and order are now combined into one atomic field.
This is part 3 of the mm subsystem overhaul.
The allocator doesn't rely on mutexes anymore and
uses individual per-order spinlocks instead.
Also, it is aware of multiple memory zones (normal
and DMA) as well as emergency reserves.
Page bitmaps take up 50 % less overhead now.
Another one of those larger endeavours that take
multiple commits. This first one introduces the
basic vm_page data structure, as well as the x86
bootstrap code for initializing it.