doc: convert UIO howto from docbook to sphinx

Converted with tmplcvt. Only some tiny things needed manual fixing.

Signed-off-by: Alexander Dahl <post@lespocky.de>
Cc: Hans-Jürgen Koch <hjk@hansjkoch.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>