[pytorch][nnc] mobile nnc backend skeleton (#56852)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56852
This is part of the changes to enable NNC AOT compilation for mobile.
It introduced a custom backend for NNC, which uses the components defined in the stacked PRs to load and execute a NNC-compiled model.
ghstack-source-id: 128285801
Test Plan:
- On X86 host:
```
buck build //xplat/caffe2/fb/lite_predictor:lite_predictor_nnc
buck-out/last/lite_predictor_nnc --model xplat/pytorch_models/build/pytorch_dev_linear/v1/nnc/compiled.pt --print_output true --input_dims '4,4' --input_type float
```
- On Android:
```
buck build fbsource//fbandroid/mode/gnustl //xplat/caffe2/fb/lite_predictor:lite_predictor_nncAndroid#android-armv7
adb push buck-out/last/lite_predictor_nncAndroid#android-armv7 /data/local/tmp
adb push xplat/pytorch_models/build/pytorch_dev_linear/v1/nnc/compiled.pt /data/local/tmp
adb shell 'cd /data/local/tmp; ./lite_predictor_nncAndroid\#android-armv7 --model compiled.pt --print_output true --input_dims "4,4" --input_type float'
```
Reviewed By: kimishpatel, raziel
Differential Revision: D27897153
fbshipit-source-id: 8e039089d1602782582747adfd75b31496b525ca
