[Runtime] Add graph_executor get_input_index API.

[huajsj]

In graph_executor use case, user can use set_input with input index to set input parameter, but there is no straight
forward way to get correct index number with input name, here provide get_input_index API to do such work.

[jcf94]

LGTM.

[comaniac]

LGTM

[tkonolige]

@huajsj Could you also add this to the VM api?

[huajsj]

@huajsj Could you also add this to the VM api?

@tkonolige, thanks for the comments, how about I use a separate PR to address this VM support issue?

[tkonolige]

@huajsj Totally fine, I don't want to block this PR. It just would be nice to have the api be the same between the graph runtime and the vm.

[huajsj]

@tkonolige, thanks for the follow up, sure, would do that.

[Lyken17]

Hi there,

It seems this commit introduces bugs when tunning models on raspberry pis. When I follow the example on auto-scheduler-tune-network-arm, I got following errors

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Traceback (most recent call last):
  File "pi_bench/tune_mbv2.py", line 143, in <module>
    tune_and_evaluate()
  File "pi_bench/tune_mbv2.py", line 126, in tune_and_evaluate
    module = graph_executor.GraphModule(rlib["default"](dev))
  File "/home/ligeng/Workspace/tvm/python/tvm/contrib/graph_executor.py", line 160, in __init__
    self._get_input_index = module["get_input_index"]
  File "/home/ligeng/Workspace/tvm/python/tvm/runtime/module.py", line 107, in __getitem__
    return self.get_function(name)
  File "/home/ligeng/Workspace/tvm/python/tvm/runtime/module.py", line 91, in get_function
    raise AttributeError("Module has no function '%s'" % name)
AttributeError: Module has no function 'get_input_index'

After I comment the 160th line in python/tvm/contrib/graph_executor.py, the tutorial runs without problem.

[tkonolige]

@Lyken17 Did you rebuild TVM on your raspberry pis? You can get this error when there is a TVM version mismatch between the remote and the host.

[Lyken17]

@tkonolige I am using the tvm with commit dbf9ce52d4e4fbcd0c1d44f6c8d05c7774dffe63 (3 days ago) on both of my host and pis.