[autockpt] make solver work on resnet.

[super-dainiu]

Append these few lines after SPMD solver. It works now.

Config:
ResNet50, bs = 512, device_mesh = [[0, 1], [2, 3]]

solver = CheckpointSolverRotor(gm.graph, free_memory=10*1024**3)
solver.print_chain()
gm.graph = solver.solve()
print(gm.code)