m68k: add Sysam AMCORE open board support

Add support for Sysam AMCORE board, an open hardware embedded Linux
board, see http://sysam.it/openzone/projects/amcore/amcore.html for
any info.

Signed-off-by: Angelo Dureghello <angelo@sysam.it>
Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>