drm/i915: disable PCH ports if needed when disabling a CRTC

drm/i915: disable PCH ports if needed when disabling a CRTC

BugLink: http://bugs.launchpad.net/bugs/791752

Disable any PCH ports associated with a pipe when disabling it.  This
should prevent transcoder disable failures due to ports still being on.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
[ickle: introduce *_PIPE_ENABLED() macro]
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

backported from commit 47a05eca72991039e788b25232061f9c9df9ec23
Signed-off-by: Keng-Yu Lin <keng-yu.lin@canonical.com>
Acked-by: Leann Ogasawara <leann.ogasawara@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>