The earlier pgtable.h tidying patch made things a bit too tidy.  Add
back a header which is needed in VMALLOC_START and friend.  Also add
back a definition of pmd_page_vaddr, which is needed on x86_64.
Signed-off-by: NJeff Dike <jdike@linux.intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>