[ide] add "ide=nodma" to documentation

Here's a quick patch to add the currently-undocumented ide=nodma option
to the Documentation/ide.txt file. Since the code does not mark this
option as obsolete as far as I can see, I can only assume that it should
be in the documentation
Signed-off-by: Vadim Lobanov <vlobanov@speakeasy.net>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

Documentation/ide.txt

@@ -297,6 +297,8 @@ Summary of ide driver parameters for kernel command line
 
  "ide=reverse"		: formerly called to pci sub-system, but now local.
 
+ "ide=nodma"		: disable DMA globally for the IDE subsystem.
+
 The following are valid ONLY on ide0, which usually corresponds
 to the first ATA interface found on the particular host, and the defaults for
 the base,ctl ports must not be altered.