m68k: fix 3 broken boards

Fix eb_cpu5282 and eb_cpu5282_internal unresolved external error.
These boards have video but don't need any ppc related
video_setmem().

Fix M53017EVB moving away embedded env to a different offset,
as in M52277EVB.

Signed-off-by: Angelo Dureghello <angelo@sysam.it>