Add dependency memory->device_context, because we now use platform::GPUPlaceGuard

paddle/memory/CMakeLists.txt

 add_subdirectory(detail)
 
 cc_library(memory SRCS memory.cc)
-cc_library(memcpy SRCS memcpy.cc)
+cc_library(memcpy SRCS memcpy.cc DEPS device_context)
 
 cc_library(paddle_memory
     DEPS
@@ -11,7 +11,6 @@ cc_library(paddle_memory
     meta_cache
     memory_block
     buddy_allocator
-    system_allocator
-    device_context)
+    system_allocator)
 
 cc_test(memory_test SRCS memory_test.cc DEPS place paddle_memory)