make CONFIG_DEBUG_PAGEALLOC universally available.

CONFIG_HIBERNATION and CONFIG_HUGETLBFS was disabling it, for no
particular reason.

If there are any unfixed bugs here we'll fix it, but do not disable
vital debugging facilities like that ..
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>