This reverts commit a88b1672.

From the origin comit log::

  The RST cpp:function handler is very pedantic: it doesn't allow any
  macros like __user on it

Since the kernel-doc parser does NOT make use of the cpp:domain, there
is no need to change the kernel-doc parser eleminating the address_space
tags.
Signed-off-by: Markus Heiser <markus.heiser@darmarIT.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>