Eliminate definition of I386_PAGE_SIZE and use NBPG instead

Cleaned up tabs vs spaces after #define to make file consistent.
Removed now unused definitions of I386_PAGE_SIZE and I386_PDR_SIZE

Note That these two where unused and had the wrong values anyway!
Changed I386_KPDES to NKPDE
Changed I386_UPDES to NUPDE

Redid constant assignments of *PTDI's to be sizeable and relative.