For the initial page tables we only need to identity map the kernel
image, the rest of the memory will be managed by the MemoryManager. The
linker script is updated to get the kernel image start and end
addresses.
The page table and page directory formats are architecture specific, so
move the headers into the Arch directory. Also move the aarch64 page
table constants from aarch64/MMU.cpp to aarch64/PageDirectory.h.
By default these 2 fields were zero, which made it rely on
implementation defined behavior whether these fields internally would be
set to the correct value. The ARM processor in the Raspberry PI (and
QEMU 6.x) would actually fixup these values, whereas QEMU 7.x now does
not do that anymore, and a translation fault would be generated instead.
For more context see the relevant QEMU issue:
- https://gitlab.com/qemu-project/qemu/-/issues/1157Fixes#14856
