drm/i915/icl: Enable DSI IO power

This patch configures mode of operation for DSI
and enable DDI IO power by configuring power well.

v2: Use for_each_dsi_port() for power get (Jani N)

Signed-off-by: Madhav Chauhan <madhav.chauhan@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1530798591-2077-5-git-send-email-madhav.chauhan@intel.com