Some of the implementations, in particular the ioremap variants, in
asm-generic/io.h are for systems without an MMU.  In order to be able to
use the generic header file for systems with an MMU, this patch wraps
these implementations in checks for CONFIG_MMU.

Tested on OpenRISC.
Signed-off-by: NJonas Bonn <jonas@southpole.se>
Cc: liqin.chen@sunplusct.com
Cc: gxt@mprc.pku.edu.cn
Acked-by: NMike Frysinger <vapier@gentoo.org>
Acked-by: NArnd Bergmann <arnd@arndb.de>