Cadence HiFi: Fix build errors for ResNet-18 and Emformer RNNT Encoder

[rascani]

Summary

Fix several HiFi build issues preventing ResNet-18 and Emformer RNNT Encoder from compiling and running on the Xtensa toolchain.

Fixes #18181

functions_hifi.yaml:

• Add quantized_max_pool2d_nchw op (NCHW variant was missing, only NHWC was registered). Uses generic fallback kernel.
• Add native_layer_norm op (needed by Emformer RNNT Encoder). Uses portable kernel.
• Fix double native:: namespace on quantized_conv1d_ncl and quantized_conv1d_nlc kernel names — codegen adds the native:: namespace automatically, so having it in the yaml produced impl::HiFi::native::native:: which failed to link.

CMakeLists.txt:

• Add op_quantized_max_pool2d_nhwc.cpp to custom_ops sources (file existed but was not compiled)
• Add generic conv1d fallback sources (op_quantized_conv1d_ncl.cpp, op_quantized_conv1d_nlc.cpp) that HiFi conv1d operators call
• Add generic op_quantized_max_pool2d.cpp for NCHW fallback
• Add portable op_native_layer_norm.cpp and normalization_ops_util.cpp

install_requirements.sh:

• Update nnlib-hifi4 SHA to 64d73d72 which adds xa_nn_elm_add_broadcast_4D_f32xf32_f32 (float broadcast add kernel used by op_add.cpp)

Authored with Claude.

Test Plan

  CXXFLAGS="-fno-exceptions -fno-rtti" cmake \
    -DCMAKE_TOOLCHAIN_FILE=./backends/cadence/cadence.cmake \
    -DCMAKE_INSTALL_PREFIX=cmake-xtensa \
    -DCMAKE_BUILD_TYPE=Release \
    -DEXECUTORCH_BUILD_EXECUTOR_RUNNER=ON \
    -DEXECUTORCH_BUILD_PTHREADPOOL=OFF \
    -DEXECUTORCH_BUILD_CPUINFO=OFF \
    -DEXECUTORCH_BUILD_CADENCE=ON \
    -DEXECUTORCH_BUILD_EXTENSION_RUNNER_UTIL=ON \
    -DEXECUTORCH_ENABLE_LOGGING=ON \
    -DEXECUTORCH_ENABLE_PROGRAM_VERIFICATION=ON \
    -DEXECUTORCH_USE_DL=OFF \
    -DEXECUTORCH_BUILD_PORTABLE_OPS=ON \
    -DEXECUTORCH_BUILD_KERNELS_LLM=OFF \
    -DPYTHON_EXECUTABLE=python3 \
    -DEXECUTORCH_NNLIB_OPT=ON \
    -DHAVE_FNMATCH_H=OFF \
    -DFLATCC_ALLOW_WERROR=OFF \
    -Bcmake-xtensa
  cmake --build cmake-xtensa --target install --config Release -j8

[pytorch-bot]

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