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>

arch/openrisc/Kconfig

@@ -1,6 +1,6 @@
 #
 # For a description of the syntax of this configuration file,
-# see Documentation/kbuild/config-language.txt.
+# see Documentation/kbuild/kconfig-language.txt.
 #
 
 config OPENRISC

arch/openrisc/include/asm/dma-mapping.h

@@ -18,7 +18,7 @@
 #define __ASM_OPENRISC_DMA_MAPPING_H
 
 /*
- * See Documentation/PCI/PCI-DMA-mapping.txt and
+ * See Documentation/DMA-API-HOWTO.txt and
  * Documentation/DMA-API.txt for documentation.
  *
  * This file is written with the intention of eventually moving over