drm/ttm: fix the warning for hit_low and evict_low

fix the below warning messages:
ttm/ttm_bo.c:1098: warning: Function parameter or struct member 'hit_low' not described in 'ttm_bo_swapout_walk'
ttm/ttm_bo.c:1098: warning: Function parameter or struct member 'evict_low' not described in 'ttm_bo_swapout_walk'

Cc: Maarten Lankhorst <dev@lankhorst.se>
Cc: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>
Reviewed-by: Maarten Lankhorst <dev@lankhorst.se>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://lore.kernel.org/r/20250423042442.762108-1-sunil.khatri@amd.com

Author: amd-sukhatri

drivers/gpu/drm/ttm/ttm_bo.c

@@ -1093,7 +1093,8 @@ struct ttm_bo_swapout_walk {
 	struct ttm_lru_walk walk;
 	/** @gfp_flags: The gfp flags to use for ttm_tt_swapout() */
 	gfp_t gfp_flags;
-
+	/** @hit_low: Whether we should attempt to swap BO's with low watermark threshold */
+	/** @evict_low: If we cannot swap a bo when @try_low is false (first pass) */
 	bool hit_low, evict_low;
 };