drm/i915: Disable LVDS port after the pipe on PCH

Follow the correct pipe vs port disable sequence for the PCH LVDS
ports, ie. disable the port after the pipe.

Other PCH port were already converted in the following commits:
 1ea56e26 drm/i915: Disable CRT port after pipe on PCH platforms
 3c65d1d1 drm/i915: Disable SDVO port after the pipe on PCH platforms
 a4790cec drm/i915: Disable HDMI port after the pipe on PCH platforms
 08aff3fe drm/i915: Move DP port disable to post_disable for pch platforms
but LVDS was forgotten.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>