drm/i915/icl: Ungate DSI clocks

Ungate the clocks on the selected port.

Signed-off-by: Madhav Chauhan <madhav.chauhan@intel.com>
Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/2a01b3158feda624f98581b780854fe3df8c328d.1543500286.git.jani.nikula@intel.com