m68k: m68328: move platform code to separate files

The dragen2 and ucsimm/ucdimm files require a bit of
custom code compared to the other dragonball platforms,
move them into separate files as a preparation for a
build fix.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>