drm: fix regression in fb blank handling

commit 731b5a15
Author: James Simmons <jsimmons@infradead.org>
Date:   Thu Oct 29 20:39:07 2009 +0000

    drm/kms: properly handle fbdev blanking

uses DRM_MODE_DPMS_ON for FB_BLANK_NORMAL, but DRM_MODE_DPMS_ON
is actually for turning output on instead of blank.

This makes fb blank broken on my T61, it put LVDS on but leave
pipe disabled which made screen totally white or caused some
'burning' effect.

[airlied: James objects to this but at this point in 2.6.33,
I can't see a patch that will fix this properly like he wants coming
in time and otherwise this is a regression - proper fix for 2.6.34
hopefully.]

Cc: James Simmons <jsimmons@infradead.org>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>