plugins/amdgpu: Implement parallel restore

This patch implements the entire logic to enable the offloading of
buffer object content restoration. It has two parts: the first replaces
the restoration of buffer objects in the target process by sending a
parallel restore command to the main CRIU process; the second implements
the `POST_FORKING` hook in the amdgpu plugin to enable buffer object
content restoration in the main CRIU process.

Signed-off-by: Yanning Yang <yangyanning@sjtu.edu.cn>

plugins/amdgpu/Makefile

@@ -27,7 +27,7 @@ endif
 criu-amdgpu.pb-c.c: criu-amdgpu.proto
 		protoc-c --proto_path=. --c_out=. criu-amdgpu.proto
 
-amdgpu_plugin.so: amdgpu_plugin.c amdgpu_plugin_drm.c amdgpu_plugin_topology.c amdgpu_plugin_util.c criu-amdgpu.pb-c.c
+amdgpu_plugin.so: amdgpu_plugin.c amdgpu_plugin_drm.c amdgpu_plugin_topology.c amdgpu_plugin_util.c criu-amdgpu.pb-c.c amdgpu_socket_utils.c
 	$(CC) $(PLUGIN_CFLAGS) $(shell $(COMPEL) includes) $^ -o $@ $(PLUGIN_INCLUDE) $(PLUGIN_LDFLAGS) $(LIBDRM_INC)
 
 amdgpu_plugin_clean: