Fix the pt_entry_t and pd_entry_t types. They were previously pointers to

Fix the pt_entry_t and pd_entry_t types.  They were previously pointers to
integers which is completely bogus.  What they really represent are page
table entries so define them as __uint32_t.  Also add a vtophys_pte()
macro to distinguish between physical addresses (vm_paddr_t) and
physical addresses represented in PTE form (pt_entry_t).  vm_paddr_t can
be 64 bits even on IA32 boxes without PAE which use 32 bit PTE's.

Taken loosely from: FreeBSD-4.x