drm: Only set DPMS ON when actually configuring a mode

In drm_crtc_helper_set_config, instead of always forcing all outputs
to DRM_MODE_DPMS_ON, only set them if the CRTC is actually getting a
mode set, as any mode set will turn all outputs on.

This fixes https://lkml.org/lkml/2011/1/24/457

Signed-off-by: Keith Packard <keithp@keithp.com>
Cc: stable@kernel.org (2.6.37)
Reported-and-tested-by: Carlos R. Mafra <crmafra2@gmail.com>
Tested-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>