For small systems we would put the zImage at 32KiB after
the start of memory, and put the DT a bit after the uImage.
The kernel will always try to relocate itself and overwrite
the DT.

Try to be more clever at uImage placement to avoid
triggering the kernel relocation.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>