drm/i915/dsi: convert to struct intel_display

struct intel_display will replace struct drm_i915_private as the main
device pointer for display code. Switch ICL DSI code over to it.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/f62a3616ef15e02cf19c5d041656fc6e09b37f6a.1730146000.git.jani.nikula@intel.com

Author: jnikula