Add CUB block and device merge sort

cub/block/block_load.cuh

@@ -34,6 +34,7 @@
 #pragma once
 
 #include <iterator>
+#include <type_traits>
 
 #include "block_exchange.cuh"
 #include "../iterator/cache_modified_input_iterator.cuh"
@@ -1284,6 +1285,17 @@ public:
 
 };
 
+template <class Policy,
+          class It,
+          class T = typename std::iterator_traits<It>::value_type>
+struct BlockLoadType
+{
+  using type = cub::BlockLoad<T,
+                              Policy::BLOCK_THREADS,
+                              Policy::ITEMS_PER_THREAD,
+                              Policy::LOAD_ALGORITHM>;
+};
+
 
 CUB_NAMESPACE_END