drm/i915: Disable CRT port after pipe on PCH platforms

Follow the BSpec sequence for the CRT port as well on PCH platforms,
ie. disable the pipe before the port.

Didn't bother looking at DDI in detail yet, so leave that one be even
though the CRT is a PCH port there.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>