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>

arch/x86/mm/iomap_32.c

@@ -68,6 +68,7 @@ out_free:
 out_err:
 	return -EINVAL;
 }
+EXPORT_SYMBOL_GPL(reserve_io_memtype_wc);
 
 void
 free_io_memtype(u64 base, unsigned long size)
@@ -75,6 +76,7 @@ free_io_memtype(u64 base, unsigned long size)
 	if (pat_enabled)
 		free_memtype(base, base + size);
 }
+EXPORT_SYMBOL_GPL(free_io_memtype);
 
 /* Map 'pfn' using fixed map 'type' and protections 'prot'
  */