Arm: Create script for model testing and split run.sh example script (#8460)

Create model test script and break up run.sh into smaller scripts that
can be used from both places.

This makes it possible to run things in run.sh in separate steps
like this:

1. Build needed libs
backends/arm/scripts/build_executorch.sh
backends/arm/scripts/build_portable_kernels.sh --portable_kernels=<OPS>
backends/arm/scripts/build_quantized_ops_aot_lib.sh

2. Build <PTE FILE>
python3 -m examples.arm.aot_arm_compiler --target=ethos-u85-128 --delegate --quantize --so_library=<PATH>/libquantized_ops_aot_lib.so --model_name=<MODEL>

3. Build target executable <ELF FILE>
backends/arm/scripts/build_executorch_runner.sh --pte=<PTE_FILE> --target=ethos-u55-128

4. Test target executable in FVP
backends/arm/scripts/run_fvp.sh --elf=<ELF_FILE> --target=ethos-u85-128

Signed-off-by: Zingo Andersen <zingo.andersen@arm.com>