ppc4xx: Unify AMCC's board config files (part 2/3)

This patch series unifies the AMCC eval board ports by introducing
a common include header for all AMCC eval boards:

include/configs/amcc-common.h

This header now includes all common configuration options/defines which
are removed from the board specific headers.

The reason for this is ease of maintenance and unified look and feel
of all AMCC boards.

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