CHROMIUM: intel_ddi: Reverse DP lanes based on polarity.

Platforms with USB type-C outputs can take advantage of GPU's builtin
DisplayPort lane reversal mux.

Note, this change affects samus only.

Signed-off-by: Todd Broch <tbroch@chromium.org>

BUG=chrome-os-partner:35351,chrome-os-partner:40076
BUG=b:123092035
TEST=manual,
Samus + hoho + Samsung U28D590 external monitor successfully drives
DP output in both polarities.  Also tested flipping polarity while in
S3.  Also compiles on x86 devices w/o cros_ec_pd.

Change-Id: I16c052c29bad1a263afeb750f54679c34ac901e0
Reviewed-on: https://chromium-review.googlesource.com/270334


Reviewed-by: Stphane Marchesin <marcheu@chromium.org>
Commit-Queue: Todd Broch <tbroch@chromium.org>
Tested-by: Todd Broch <tbroch@chromium.org>
[jflat: cleaned up and moved changes into intel_ddi_pre_enable_dp]
Signed-off-by: Jon Flatley <jflat@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1423679


Reviewed-by: Dmitry Torokhov <dtor@chromium.org>