Overhaul memory allocation model

This commit makes several fundamental changes to memory handling:

- the frame allocator is now only an allocator for free frames, and does
  not track used frames.
- the frame allocator now stores its free list inside the free frames
  themselves, as a hybrid stack/span model.
  - This has the implication that all frames must currently fit within
    the offset area.
- kutil has a new allocator interface, which is the only allowed way for
  any code outside of src/kernel to allocate. Code under src/kernel
  _may_ use new/delete, but should prefer the allocator interface.
- the heap manager has become heap_allocator, which is merely an
  implementation of kutil::allocator which doles out sections of a given
  address range.
- the heap manager now only writes block headers when necessary,
  avoiding page faults until they're actually needed
- page_manager now has a page fault handler, which checks with the
  address_manager to see if the address is known, and provides a frame
  mapping if it is, allowing heap manager to work with its entire
  address size from the start. (Currently 32GiB.)

src/kernel/device_manager.h

@@ -2,14 +2,13 @@
 /// \file device_manager.h
 /// The device manager definition
 #include "kutil/vector.h"
+#include "apic.h"
 #include "pci.h"
 
 struct acpi_xsdt;
 struct acpi_apic;
 struct acpi_mcfg;
 class block_device;
-class lapic;
-class ioapic;
 
 using irq_callback = void (*)(void *);
 
@@ -19,8 +18,9 @@ class device_manager
 {
 public:
 	/// Constructor.
-	/// \arg root_table   Pointer to the ACPI RSDP
-	device_manager(const void *root_table);
+	/// \arg root_table  Pointer to the ACPI RSDP
+	/// \arg alloc       Allocator for device arrays
+	device_manager(const void *root_table, kutil::allocator &alloc);
 
 	/// Get the system global device manager.
 	/// \returns  A reference to the system device manager
@@ -105,7 +105,7 @@ private:
 	void bad_irq(uint8_t irq);
 
 	lapic *m_lapic;
-	kutil::vector<ioapic *> m_ioapics;
+	kutil::vector<ioapic> m_ioapics;
 
 	kutil::vector<pci_group> m_pci;
 	kutil::vector<pci_device> m_devices;