Remove tracking of sMaxVirtualAddress as it's not used.

The value computed isn't actually used anywhere. It just ensured that
a panic would be triggered if we "skipped" to virtual addresses further
along. This shouldn't be problematic however.

Reuse get_or_create_page_table() and remove similar add_page().

The former also does the initialization, simplifying the code and
reducing redundancy with the page directory init path.

Clear the page tables on creation, use macros for counts.

This makes it less likely that uninitialized entries cause troubles.
Also panic if we encounter an unknown entry type instead of defaulting
to 4K pages.

Simplify the page directory init loops.

Also check and possibly reuse an existing page directory entry. This
makes the possible memory maps a little more flexible.

Header cleanup, rename macros for more consistency.

Map the page directory before turning on the MMU.

And actually use the virtual address for it later on. This wasn't
problematic as the virtual and physical addresses are identity mapped,
but it seems more correct to do it in this order.

Simplify, don't do the calculation twice.

Style cleanup only.

Fix more format strings for MMU trace output.

Fix warnings by using format macros in debug output.

Merge common ARM CPU/MMU code

This is to make sure all ARM platforms will benefit from planned work on this
MMU/CPU code. The less code duplicated, the better.

Compile-tested for all supported ARM platforms

Merge common ARM CPU/MMU code

This is to make sure all ARM platforms will benefit from planned work on this
MMU/CPU code. The less code duplicated, the better.

Compile-tested for all supported ARM platforms