The current eva_ramboot.py script is currently only compatible with
Lantiq based AVM devices. For IPQ40xx devices, the offset needs to be
changed. Also an alignment is not necessary here.

Adjust the script to be able to pass an optional offset to load the
image to. In case no offset is provided, the script behaves exactly as
before this commit.

Signed-off-by: David Bauer <mail@david-bauer.net>