[nnc] Limit the number of inputs to a fusion group.
Summary:
nvrtc has a hard limit to the size of kernel parameters, and llvm has
a tendency to OOM with huge parameter lists, so let's limit the number of
inputs to something sensible.
Test Plan:
tested on pyper OOM test case:
```
flow-cli test-locally --mode=opt-split-dwarf f278102738 --name "PyPer OOM repro f277966799 f63b1f9c5c0c" --run-as-secure-group oncall_pytorch_jit --entitlement default
```
Reviewed By: ZolotukhinM
Differential Revision: D29019751
fbshipit-source-id: b27f2bb5000e31a7b49ea86a6928faa0ae2ead24
