The page table walker provides a mechanism for accessing the individual
page table entries that correspond to a particular virtual memory
address. This implementation will serve as the basis for implementing
page mapping/unmapping and virtual to physical address translation.
This is equivalent to pmm.Frame (also a uintptr) but having different
types for physical and virtual frames serves as an additional layer of
protection for functions/methods that receive physical and/or virtual
page arguments.
To keep the implementation portable, the Frame type had to be changed
from uint64 to uintptr. Using uintptr ensures that the frame will always
match the pointer size of the platform.
