i915: Added function to initialize VBT settings

Added a function that sets the LVDS values to default settings.  This
will be called by intel_init_bios before checking for the VBT (video BIOS
table). The default values are thus loaded regardless of whether a VBT
is found.

The default settings in each parse function have been moved to the new
function. This consolidates all the default settings into one place.

The default dither bit value has been changed from 0 to 1.  We can
assume that display devices will want dithering enabled.

Signed-off-by: Simon Que <sque@chromium.org>
Acked-by: Olof Johansson <olof@lixom.net>
[ickle: fixup for -next]
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>