drm/i915: move and group hdcp under display.hdcp

Move display hdcp related members under drm_i915_private display
sub-struct.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1083f5a58cce1507bd19bf7f98bf85e9351b741e.1661779055.git.jani.nikula@intel.com