Add kDLAscend for Huawei Ascend NPU device memory (#189)

This can be used to exchange buffers between Ascend integrations such as
torch_npu, TVM-FFI, and TileLang without overloading kDLExtDev.
kDLExtDev is shared by unrelated extension backends and cannot uniquely
identify Ascend device memory.

Author: voidLitchi

include/dlpack/dlpack.h

@@ -124,6 +124,8 @@ typedef enum {
   kDLTPU = 19,
   /*! \brief Google TPU Host device (pinned memory) */
   kDLTPUHost = 20,
+  /*! \brief Huawei Ascend NPU device */
+  kDLAscend = 21,
 } DLDeviceType;
 
 /*!