Pagetables to use normal kernel types

This is my first step in the migration of page_tables.c to the kernel
types and functions/macros (2.6.23-rc3).  Seems to be working OK.

Signed-off-by: Matias Zabaljauregui <matias.zabaljauregui@cern.ch>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>