drm/i915/icl: Configure lane sequencing of combo phy transmitter

This patch set the loadgen select and latency optimization for
aux and transmit lanes of combo phy transmitters. It will be
used for MIPI DSI HS operations.

v2: Rebase
v3: Add empty line to make code more legible (Ville).

Signed-off-by: Madhav Chauhan <madhav.chauhan@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1537095223-5184-2-git-send-email-madhav.chauhan@intel.com