PCI: handle PCI state saving with interrupts disabled

Since interrupts will soon be disabled at PCI resume time, we need to
pre-allocate memory to save/restore PCI config space (or use GFP_ATOMIC,
but this is safer).

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>