drm/i915/cx0: convert to struct intel_display

struct intel_display will replace struct drm_i915_private as the main
device pointer for display code. Switch Cx0 PHY code over to it.

v2: Rebase, split out the include cleanups (Rodrigo)

v3: Rebase

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241029160822.800097-1-jani.nikula@intel.com