drm/i915/dsi: Gate DSI clocks earlier

The clock gating step is in the wrong spot compared to the
TGL+ bspec sequence. Move it the right place. Windows also
seems to use the TGL+ order here always.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230608203057.23759-6-ville.syrjala@linux.intel.com