drm/radeon: only add the mm i2c bus if the hw_i2c module param is set

drm/radeon: only add the mm i2c bus if the hw_i2c module param is set

commit 46783150a6552f9513f08e62cfcc07125d6e502b upstream.

It seems it can corrupt the monitor EDID in certain cases on certain
boards when running sensors detect.  It's rarely used anyway outside
of AIW boards.

http://lists.lm-sensors.org/pipermail/lm-sensors/2012-April/035847.html
http://lists.freedesktop.org/archives/xorg/2011-January/052239.html

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>