Arm backend: Make aot_arm_compiler.py functions importable (#18039)

Calibration was tied to the ImageNet evaluator, so when the evaluation
feature was removed from aot_arm_compiler.py, custom calibration of a
quantized model was no longer possible.

This patch reimplements quantization calibration into
aot_arm_compiler.py, but it is instead controlled by a flag called
--calibration_data. This flag can target a file that is either a common
image format, a serialized file (.pt), or a directory which will make
the program search for applicable files within the directory.

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils
@Sebastian-Larsson @robell

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Signed-off-by: Martin Lindström <Martin.Lindstroem@arm.com>
Co-authored-by: Martin Lindström <Martin.Lindstroem@arm.com>
Co-authored-by: Zingo Andersen <zingo.andersen@arm.com>

Author: 3 people