drm/xe/guc: Update few GuC CTB ABI definitions

In upcoming new GuC ABI definitions we will want to refer to max
number of dwords that could fit into CTB HXG message. Add explicit
definition named as GUC_CTB_MAX_DWORDS and start using it.
Reviewed-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Link: https://lore.kernel.org/r/20240104222031.277-6-michal.wajdeczko@intel.comSigned-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>

drivers/gpu/drm/xe/abi/guc_communication_ctb_abi.h

@@ -81,12 +81,13 @@ static_assert(sizeof(struct guc_ct_buffer_desc) == 64);
 
 #define GUC_CTB_HDR_LEN				1u
 #define GUC_CTB_MSG_MIN_LEN			GUC_CTB_HDR_LEN
-#define GUC_CTB_MSG_MAX_LEN			256u
+#define GUC_CTB_MSG_MAX_LEN			(GUC_CTB_MSG_MIN_LEN + GUC_CTB_MAX_DWORDS)
 #define GUC_CTB_MSG_0_FENCE			(0xffff << 16)
 #define GUC_CTB_MSG_0_FORMAT			(0xf << 12)
 #define   GUC_CTB_FORMAT_HXG			0u
 #define GUC_CTB_MSG_0_RESERVED			(0xf << 8)
 #define GUC_CTB_MSG_0_NUM_DWORDS		(0xff << 0)
+#define   GUC_CTB_MAX_DWORDS			255
 
 /**
  * DOC: CTB HXG Message