drm/xe/hdcp: Enable HDCP for XE

Enable HDCP for Xe by defining functions which take care of
interaction of HDCP as a client with the GSC CS interface.
Add intel_hdcp_gsc_message to Makefile and add corresponding
changes to xe_hdcp_gsc.c to make it build.

--v2
-add kfree at appropriate place [Daniele]
-remove useless define [Daniele]
-move host session logic to xe_gsc_submit.c [Daniele]
-call xe_gsc_check_and_update_pending directly in an if condition
[Daniele]
-use xe_device instead of drm_i915_private [Daniele]

--v3
-use xe prefix for newly exposed function [Daniele]
-remove client specific defines from intel_gsc_mtl_header [Daniele]
-add missing kfree() [Daniele]
-have NULL check for hdcp_message in finish function [Daniele]
-dont have too many variable declarations in the same line [Daniele]

--v4
-don't point the hdcp_message structure in xe_device to anything
until it properly gets initialized [Daniele]

--v5
-Squash commits for buildability

--v6
-Order includes alphabetically [Lucas]

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/20240306024247.1857881-6-suraj.kandpal@intel.com