ktn-mx8mm.inc: Align ARM64 image entrypoint to 0x200000

This change is not compatible with Kernel versions below 5.8. For 5.8 and later it prevents the following warning:

[Firmware Bug]: Kernel image misaligned at boot, please fix your bootloader!

This intends to solve https://git.kontron-electronics.de/sw/ked/plan/plan-yocto/-/issues/999.