drm/i915/sdvo: force GPIO bit-banging also on default pin

drm/i915/sdvo: force GPIO bit-banging also on default pin

commit 63abf3edaf42d0b9f278df90fe41c7ed4796b6b1
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Wed Dec 8 16:48:21 2010 +0000

    drm/i915/sdvo: Only use the SDVO pin if it is in the valid range

added a default fallback if BIOS provides an invalid pin mapping, but
failed to force GPIO bit-banging on it. Finish the job, and also clean up
the function a bit. With bit-banging, setting the gmbus speed has no
effect, so drop it.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
[danvet: Extend comment about gmbus in the code a bit.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>