Switch page_manager to use frame_allocator.

Removed the frame allocation logic from page_manager and replaced it
with using an instance of frame_allocator instead. This had several
major ripple effects:

- memory_initalize() had to change to support this new world
  - Where to map used blocks is now passed as a flag, since blocks don't
    track their virtual address anymore
  - Instead of the complicated "find N contiguous pages that can be
    mapped in with one page table", we now just have the bootloader give
    us some (currently 64) pages to use both for tables and scratch
    space.
  - frame_allocator initialization was split into two steps to allow
    mapping used blocks before std::move()ing them over

src/boot/loader.h

@@ -12,18 +12,6 @@
 #define KERNEL_VIRT_ADDRESS 0xFFFFFF0000000000
 #endif
 
-#ifndef KERNEL_MEMTYPE
-#define KERNEL_MEMTYPE static_cast<EFI_MEMORY_TYPE>(0x80000000)
-#endif
-
-#ifndef INITRD_MEMTYPE
-#define INITRD_MEMTYPE static_cast<EFI_MEMORY_TYPE>(0x80000001)
-#endif
-
-#ifndef KERNEL_DATA_MEMTYPE
-#define KERNEL_DATA_MEMTYPE static_cast<EFI_MEMORY_TYPE>(0x80000002)
-#endif
-
 #ifndef KERNEL_FILENAME
 #define KERNEL_FILENAME L"kernel.elf"
 #endif