Arm backend: Add LSTM test for int16x8

[SaoirseARM]

Summary

Adds testcases to LSTM model unit test for in16x8 support

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/15524

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⏳ 1 Pending, 6 Unrelated Failures

As of commit 468cabe with merge base 2aeee9b ():

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

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

• pull / unittest / linux / linux-job (gh) (trunk failure)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_int8_static_quant_recipe
• pull / unittest / macos / macos-job (gh) (trunk failure)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_int8_static_quant_recipe
• pull / unittest-editable / linux / linux-job (gh) (trunk failure)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_int8_static_quant_recipe
• pull / unittest-editable / macos / macos-job (gh) (trunk failure)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_int8_static_quant_recipe
• trunk / unittest-release / linux / linux-job (gh) (trunk failure)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_int8_static_quant_recipe
• trunk / unittest-release / macos / macos-job (gh) (trunk failure)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_int8_static_quant_recipe

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[SaoirseARM]

@pytorchbot label 'partner: arm'

[SaoirseARM]

@pytorchbot label ciflow/trunk

[SaoirseARM]

@pytorchbot label "release notes: none"

[Ninja91]

LGTM!

[zingo]

Seem to fail :(
FAILED backends/arm/test/models/test_lstm_arm.py::test_lstm_16a8w_tosa_INT
FAILED backends/arm/test/models/test_lstm_arm.py::test_lstm_16a8w_u85_INT

[zingo]

Seem to fail :( FAILED backends/arm/test/models/test_lstm_arm.py::test_lstm_16a8w_tosa_INT FAILED backends/arm/test/models/test_lstm_arm.py::test_lstm_16a8w_u85_INT

Might gone away after rebase, or it's flakey error, Ill tests a new rebase to retrigger a test run.