* [fx] allow control of ckpt_codegen init
Currently in ColoGraphModule, ActivationCheckpointCodeGen will be set automatically in __init__. But other codegen can't be set if so.
So I add an arg to control whether to set ActivationCheckpointCodeGen in __init__.
* code style
* [fx] add input activation offload to codegen
* [fx] modify unit test
* [fx] remove two skips in torch11
* [fx] use all_input_nodes instead of _input_nodes