nnlib-hifi4 is too big during setting up ExecuTorch from source

[mergennachin]

🚀 The feature, motivation and pitch

During slow internet connection, it takes a long time to set up ExecuTorch. This is due to download all gitsubmodules. Here's the root level filesizes (after git submodule sync; git submodule update --init)

708M	backends/
172K	build/
128K	codegen/
 12K	configurations/
540K	devtools/
 31M	docs/
 59M	examples/
2.3M	exir/
 74M	extension/
 24M	kernels/
 40K	profiler/
1.4M	runtime/
 60K	schema/
 32K	scripts/
176K	shim/
168K	test/
 42M	third-party/
 24K	util/

Within backends/ folder, here's the breakdown:

1.6M	apple/
4.2M	arm/
485M	cadence/
960K	example/
228K	mediatek/
1.3M	qualcomm/
 96K	transforms/
 23M	vulkan/
192M	xnnpack/

The main culprit is this library: https://github.com/pytorch/executorch/tree/main/backends/cadence/hifi/third-party/nnlib

Is it possible move cadence related to installation into its own set up script, like we do for other backends like coreml? For example: https://github.com/pytorch/executorch/blob/main/backends/apple/coreml/scripts/install_requirements.sh

Alternatives

No response

Additional context

No response

RFC (Optional)

No response

[mcremon-meta]

That should be possible. We can take a look as soon as some current urgent work is wrapped up, most likely next week!