drm/i915/display: Add definition for wcl as subplatform

drm/i915/display: Add definition for wcl as subplatform

We will need to differentiate between WCL and PTL in
intel_encoder_is_c10phy(). Since WCL and PTL use the same display
architecture, let's define WCL as a subplatform of PTL to allow the
differentiation.

v2: Update commit message and reorder wcl define (Gustavo)

Fixes: 3c0f211bc8fc ("drm/xe: Add Wildcat Lake device IDs to PTL list")
Signed-off-by: Dnyaneshwar Bhadane <dnyaneshwar.bhadane@intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://lore.kernel.org/r/20250922150317.2334680-3-dnyaneshwar.bhadane@intel.com
(cherry picked from commit 4dfaae643e59cf3ab71b88689dce1b874f036f00)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
[Rodrigo added Fixes tag when porting it to fixes]