Limitations present when interacting with 32-bit U-Boot on 64-bit ARMv8 device

[jynik]

Refer to #3 for more information: https://github.com/nccgroup/depthcharge/issues/3#issuecomment-866885873

Users can use --arch arm for such devices, but will not be able to perform operations that necessitate triggering data aborts; attempts to do so via unaligned accesses will fail. This amounts to not using the -R, --allow-reboot option when attempting to interact with a 32-bit U-Boot build on an ARMv8 device.