drm/i915: rip out intel_disable_pch_ports

Even with the old crtc helper code we should have disabled all
encoders on that pipe by now, and with the new code this would
definitely paper over a bug. We already have the necessary checks
in place in intel_disable_transcoder, so if we accidentally leave
a pch port on, this will be caught.

Hence just rip this all out.

Note that up to the patch in this giant modeset series that removes
the LVDS special case to avoid disabling LVDS in the encoder->prepare
callback ("drm/i915/lvds: ditch ->prepare special case"), this was not
the case for all outputs.

Also note that in

commit 1b3c7a47
Author: Zhenyu Wang <zhenyuw@linux.intel.com>
Date:   Wed Nov 25 13:09:38 2009 +0800

    drm/i915: Fix LVDS stability issue on Ironlake

this was already discovered independently and worked around. How I
bloody hate this entire mess of cludges piled on top of other cludges.

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>