drm/i915/dpio: convert to struct intel_display

struct intel_display will replace struct drm_i915_private as the main
device pointer for display code. Switch DPIO PHY 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/1138083101f3c9058284592009b25f41065fbe30.1730146000.git.jani.nikula@intel.com