These images have to be located in the first 128MB of SDRAM, so
use the following strategy:

- first try to map the image. If the pointer is within the first
  128MB of sdram everything is fine.
- if we can't map the image, check for SDRAM being smaller than
  128MB we can use malloc for allocating space for the image.
- As a last fallback we simply put the image to 8MB into SDRAM.
  This is not very clean. We try our best by checking that we
  won't overwrite the malloc space.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>