drm/loongson: use GEM references instead of TTMs

Instead of a TTM reference grab a GEM reference whenever necessary.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sui Jingfeng <suijingfeng@loongson.cn>
Link: https://patchwork.freedesktop.org/patch/msgid/20240723121750.2086-3-christian.koenig@amd.com

drivers/gpu/drm/loongson/lsdc_ttm.c

@@ -341,16 +341,12 @@ void lsdc_bo_unpin(struct lsdc_bo *lbo)
 
 void lsdc_bo_ref(struct lsdc_bo *lbo)
 {
-	struct ttm_buffer_object *tbo = &lbo->tbo;
-
-	ttm_bo_get(tbo);
+	drm_gem_object_get(&lbo->tbo.base);
 }
 
 void lsdc_bo_unref(struct lsdc_bo *lbo)
 {
-	struct ttm_buffer_object *tbo = &lbo->tbo;
-
-	ttm_bo_put(tbo);
+	drm_gem_object_put(&lbo->tbo.base);
 }
 
 int lsdc_bo_kmap(struct lsdc_bo *lbo)