gpu/drm, x86, PAT: PAT support for io_mapping_*, export symbols for modules

Impact: build fix

 ERROR: "reserve_io_memtype_wc" [drivers/gpu/drm/i915/i915.ko] undefined!
 ERROR: "free_io_memtype" [drivers/gpu/drm/i915/i915.ko] undefined!

Signed-off-by: Ingo Molnar <mingo@elte.hu>