m68k: add Sysam stmark2 open board support

Add support for Sysam stmark2 board, an open hardware embedded
Linux board, see http://sysam.it/cff_stmark2.html

 for any info.

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