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>
diff --git a/drivers/video/igafb.c b/drivers/video/igafb.c
index d885c77..2d97752 100644
--- a/drivers/video/igafb.c
+++ b/drivers/video/igafb.c
@@ -428,7 +428,7 @@
 	 *
 	 * IGS2000 has its I/O memory mapped and we want
 	 * to generate memory cycles on PCI, e.g. do ioremap(),
-	 * then readb/writeb() as in Documentation/IO-mapping.txt.
+	 * then readb/writeb() as in Documentation/io-mapping.txt.
 	 *
 	 * IGS1682 is more traditional, it responds to PCI I/O
 	 * cycles, so we want to access it with inb()/outb().