drm/i915/bios: Change default clock source on PineView to use SSC

The i915 driver normally assumes the video bios has configured several
of the LVDS panel registers, and it just inherits the values. If the
vbios has not run, several of these will need to be setup.

If these are not correct then although the panel looks ok, output from an
HDMI encoder (eg, Chrontel CH7036) will be incorrect.

Signed-off-by: Mark Hayter <mdhayter@chromium.org>
[ickle: minor adjustments]
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>