include/linux/pgtable.h: convert arch_enter_lazy_mmu_mode() and friends to static inlines

For all the usual reasons, plus a new one.  Calling

	(void)arch_enter_lazy_mmu_mode();

deservedly blows up.

Cc: Balbir Singh <balbirs@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>