soc: intel_adsp: Use build system Python to run fix_elf_addrs.py

This commit updates the intel_adsp build script to invoke the
`fix_elf_addrs.py` Python script using the Python executable detected
by the build system.

This ensures that the script is run using the same Python installation
used by the Zephyr build system.

Signed-off-by: Stephanos Ioannidis <stephanos.ioannidis@nordicsemi.no>