drm/i915: Allow PCH platforms fall back to BIOS LVDS mode

With intel_encoder_current_mode() using the normal state readout code it
actually works on PCH platforms as well. So let's nuke the PCH check from
intel_lvds_init(). I suppose there aren't any machines that actually
need this, but at least we get to eliminate a few lines of code, and one
FIXME.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171009161951.22420-2-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>