drm/i915: Fix LVDS stability issue on Ironlake

In disable sequence, all output ports on PCH have to be disabled
before PCH transcoder, but LVDS port was left always enabled. This
one fixes that by disable LVDS port properly during pipe disable
process, and resolved stability issue seen on Ironlake. Also move
panel fitting disable time just after pipe disable to align with
the spec.

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>