drm/radeon/kms: add hw_i2c module option

Turn off hw i2c by default except for mm i2c which
is hw only until we sort out the remaining prescale
issues on older chips.  hw i2c can be enabled with
hw_i2c=1.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/radeon.h b/drivers/gpu/drm/radeon/radeon.h
index 1710b9e..034218c 100644
--- a/drivers/gpu/drm/radeon/radeon.h
+++ b/drivers/gpu/drm/radeon/radeon.h
@@ -92,6 +92,7 @@
 extern int radeon_dynpm;
 extern int radeon_audio;
 extern int radeon_disp_priority;
+extern int radeon_hw_i2c;
 
 /*
  * Copy from radeon_drv.h so we don't have to include both and have conflicting