drm/i915/hdcp: split HDCP GSC message alloc/save responsibilities

drm/i915/hdcp: split HDCP GSC message alloc/save responsibilities

Allocate and initialize the HDCP GSC message in
intel_hdcp_gsc_hdcp2_init() as before, but store the pointer to
display->hdcp.hdcp_message in the caller. Similarly, pass in the pointer
to intel_hdcp_gsc_free_message().

Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://lore.kernel.org/r/a74fcc941126bf92d12115b5faf4f75099e26242.1745524803.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>