m68knommu: user generic iomap to support ioread*/iowrite*

There is no reason we cannot use the generic iomap support to give us
the ioread* and iowrite* family of IO access functions. The m68k arch with
MMU enabled does, so this makes us consistent for all m68k now.

Some potentially valid drivers will fail to compile without these,
for example:

drivers/i2c/busses/i2c-ocores.c:81:2: error: implicit declaration of
function ‘iowrite8’ [-Werror=implicit-function-declaration]
drivers/i2c/busses/i2c-ocores.c:86:2: error: implicit declaration of
function ‘iowrite16’ [-Werror=implicit-function-declaration]
drivers/i2c/busses/i2c-ocores.c:91:2: error: implicit declaration of
function ‘iowrite32’ [-Werror=implicit-function-declaration]
drivers/i2c/busses/i2c-ocores.c:96:2: error: implicit declaration of
function ‘ioread8’ [-Werror=implicit-function-declaration]
drivers/i2c/busses/i2c-ocores.c:101:2: error: implicit declaration of
function ‘ioread16’ [-Werror=implicit-function-declaration]
drivers/i2c/busses/i2c-ocores.c:106:2: error: implicit declaration of
function ‘ioread32’ [-Werror=implicit-function-declaration]

Signed-off-by: Greg Ungerer <gerg@uclinux.org>