drm/xe/hdcp: Use xe_device struct

Use xe_device struct instead of drm_i915_private so as to not
cause confusion and comply with Xe standards as drm_i915_private is
xe_device under the hood.

--v2
-Fix commit message [Daniele]

Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240306024247.1857881-4-suraj.kandpal@intel.com