drm/i915/display: Use struct intel_display instead of struct drm_i915_private

Let's start using struct intel_display instead of struct drm_i915_private
when introducing new code. No functional changes.

v2: Drop tc_to_intel_display() helper function (Jani)

Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Reviewed-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241127073200.124907-3-mika.kahola@intel.com