uml: 64-bit tlb fixes

Some 64-bit tlb fixes -
	moved pmd_page_vaddr to pgtable.h since it's the same for both
2-level and 3-level page tables
	fixed a bogus cast on pud_page_vaddr
	made the address checking in update_*_range more careful

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>