Insert PTEs for 16 mb of kernel memory.

Insert PTEs for 16 mb of kernel memory.
Added function to insert PTEs in mmu.c
mboot: complete the jump to kernel space.
mach: add some memory to our initial map.
 - We should allow freeldr's mm to request more memory before giving up
 - We'll do well to allocate big blocks directly from ofw and small blocks
   from this heap implementation
 - We can't return *all* memory like it wants because we still need ofw,
   which may need to do allocation itself

svn path=/branches/powerpc/; revision=24045