Move the mmu_initial_mapping from platform into arch/x86. For this
architecture the default mappings are basically hard coded in arch/x86
anyway, so move ownership of this data there, closer to where it's
actually initialized.
Update the 32 and 64bit paging code to properly use the paddr_to_kvaddr
and vice versa routines.
Update to allocate page tables directly from the pmm instead of the heap
(on 32bit code).
bcfad25587