drm/i915: Enable MIPI port before the plane and pipe enable

As per the hw team's recommendation we need to enable the MIPI port
before enabling the plane and pipe. So call MIPI port enable in
pre_enable phase itself

Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>