[XPU] Add docs for gm_default_size and fix type (#1962)

Add description of gm_default_size and change kunlunxin_gm_default_size‘s type to int64_t

csharp/fastdeploy/runtime_option.cs

@@ -103,6 +103,7 @@ public class RuntimeOption {
   /// \param adaptive_seqlen Is the input of multi_encoder variable length
   /// \param enable_multi_stream Whether to enable the multi stream of
   ///        KunlunXin XPU.
+  /// \param gm_default_size The default size of context global memory of KunlunXin XPU.
   ///
   public void
   UseKunlunXin(int kunlunxin_id = 0, int l3_workspace_size = 0xfffc00,