tile: handle super huge pages in virt_to_pte

This tile-specific API had a minor bug, in that if a super huge (>4GB)
page mapped a particular address range, we wouldn't handle it correctly.
As part of fixing that bug, I also cleaned up some of the pud and pmd
accessors to make them more consistent.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

diff --cc arch/tile/include/asm/pgtable_32.h
Simple merge

diff --cc arch/tile/include/asm/pgtable_64.h
Simple merge

diff --cc arch/tile/mm/pgtable.c
Simple merge