doc: fix broken references

There are numerous broken references to Documentation files (in other
Documentation files, in comments, etc.). These broken references are
caused by typo's in the references, and by renames or removals of the
Documentation files. Some broken references are simply odd.

Fix these broken references, sometimes by dropping the irrelevant text
they were part of.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/PCI/pci.txt

@@ -314,7 +314,7 @@ from the PCI device config space. Use the values in the pci_dev structure
 as the PCI "bus address" might have been remapped to a "host physical"
 address by the arch/chip-set specific kernel support.
 
-See Documentation/IO-mapping.txt for how to access device registers
+See Documentation/io-mapping.txt for how to access device registers
 or device memory.
 
 The device driver needs to call pci_request_region() to verify