Fix qnn in android demo app

[cccclai]

To build the app:

 sh scripts/build_android_library.sh

The default SeqLen is defined in https://github.com/meta-pytorch/executorch-examples/blob/9fc32b14dd91908ae5b0217e3712cda1546579f0/llm/android/LlamaDemo/app/src/main/java/com/example/executorchllamademo/MainActivity.java#L815

For QNN model, it can support up to 512 for the precompiled model.

[pytorch-bot]

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❌ 2 New Failures, 3 Unrelated Failures

As of commit 50a7cac with merge base 419727c ():

NEW FAILURES - The following jobs have failed:

• pull / unittest-arm-backend-with-no-fvp (test_pytest_models) / linux-job (gh)
  RuntimeError: Command docker exec -t 50a864ff1b3539fca55017536abced29d29b413966f834e05b668815f25f7534 /exec failed with exit code 1
• pull / unittest-nxp-neutron / linux-job (gh)
  RuntimeError: Command docker exec -t eda9ec2100d175140489daaccff63a438d1f69dd39e753866bb1d029b3de2a6c /exec failed with exit code 1

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / android / run-emulator (gh) (trunk failure)
  The process '/usr/bin/sh' failed with exit code 255
• pull / unittest / linux / linux-job (gh) (trunk failure)
• pull / unittest-editable / linux / linux-job (gh) (trunk failure)

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[cccclai]

Replace the model name here accordingly, available path is

executorch/examples/qualcomm/oss_scripts/llama/runner/runner.cpp

Line 121 in f80916e

if (decoder_model_version == "llama2") {