Revert "coredump: ARM: Ensure sp in dump is set as gdb expects"

This reverts commit ec7943bb.
This commit introduced a regression.
Let's revert it so we do not block development in main.
For more information see:
https://github.com/zephyrproject-rtos/zephyr/issues/79594



Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>