drm/i915/hdcp: further conversion to struct intel_display

There are some unconverted stragglers left in the HDCP API still using
struct drm_i915_private. Convert to struct intel_display.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/9680cc9e5ed7798a736fa73ad9ea0eb9c88e64bb.1730146000.git.jani.nikula@intel.com