I forgot to account for tracking page table physical addresses, so
this is a bit of an overhaul. Major changes:
- Refactor bootstrap code into more functions and:
- Only allocate 32 pages of scratch space
- Remap remaining space into top 256GiB, the "page table space"
- Use the page table space to directly offset-map page table pages
from their physical addresses, to avoid tracking overhead.
- Refactor page_block list functions into static functions to better
handle null/empty lists
Move EFI-related code and initial memory manager bootstrap code
to memory_bootstrap.cpp, move memory page structs to their own
memory_page.h/cpp files.
Return to having the bootloader re-map the kernel into the higher
half before jumping into the kernel entrypoint, so we don't have
to juggle pointers inside the kernel.
