ppc4xx: acadia: Add fdt support and fix section overlap problem

ppc4xx: acadia: Add fdt support and fix section overlap problem

This patch adds fdt (flattened device tree) support to the AMCC
Acadia eval board. This increases the image size and it doesn't
fit anymore into 256kByte. Since we didn't want to remove features
from the configuration, we decided to increase the U-Boot image size
(add one flash sector).

Also changed the default environment definition to make it
independent of such changes.

Signed-off-by: Stefan Roese <sr@denx.de>