soc: intel_adsp: tools: cavstool.py: argsparse code to separate function

Do not force argsparse code to all modules importing cavstool.py. The
commit moves argparse code into a separate function, and calls it from
'if __name__ == "__main__":'. Also adds the argsparse call to to
acetool.py that shares cavstool code with the argument parsing.

Signed-off-by: Jyri Sarha <jyri.sarha@linux.intel.com>