x86: paging code rewrite

The x86 paging code has been rewritten to support another paging mode
and non-identity virtual mappings.

 - Paging code now uses an array of paging level characteristics and
   walks tables using for loops. This is opposed to having different
   functions for every paging level and lots of #ifdefs. The code is
   now more concise and adding new paging modes should be trivial.

 - We now support 32-bit, PAE, and IA-32e page tables.

 - The page tables created by gen_mmu.py are now installed at early
   boot. There are no longer separate "flat" page tables. These tables
   are mutable at any time.

 - The x86_mmu code now has a private header. Many definitions that did
   not need to be in public scope have been moved out of mmustructs.h
   and either placed in the C file or in the private header.

 - Improvements to dumping page table information, with the physical
   mapping and flags all shown

 - arch_mem_map() implemented

 - x86 userspace/memory domain code ported to use the new
   infrastructure.

 - add logic for physical -> virtual instruction pointer transition,
   including cleaning up identity mappings after this takes place.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>