x86: un-__init fill_pud/pmd/pte

They are used by __set_fixmap->set_pte_vaddr_pud, which can
be used by arch_setup_additional_pages(), and so is used
after init.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>