There is no need to define map_io only for debug_ll_io_init() since it
is already called in devicemaps_init() if map_io is NULL.

Apart from that, for NOMMU build debug_ll_io_init() is a nop which
leads to following error:

CC      arch/arm/mach-imx/mach-imx1.o
arch/arm/mach-imx/mach-imx1.c:40:13: error: 'debug_ll_io_init' undeclared here (not in a function)
  .map_io  = debug_ll_io_init,
             ^
make[1]: *** [arch/arm/mach-imx/mach-imx1.o] Error 1

Cc: Alexander Shiyan <shc_work@mail.ru>
Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>