PCI: doc/pci: create Documentation/PCI/ and move files into it

Create Documentation/PCI/ and move PCI-related files to it.
Fix a few instances of trailing whitespace.
Update references to the new file locations.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index 1f506f7..e5a819a 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -430,8 +430,8 @@
 
 	[*] For information on bus mastering DMA and coherency please read:
 
-	    Documentation/pci.txt
-	    Documentation/DMA-mapping.txt
+	    Documentation/PCI/pci.txt
+	    Documentation/PCI/PCI-DMA-mapping.txt
 	    Documentation/DMA-API.txt