hw/m68k/mcf5208: Support loading of bios images

hw/m68k/mcf5208: Support loading of bios images

The MCF5208EVB supports 2 MiB of flash at address 0. Add support
for this memory region and some code to load the file that can
be specified with the "-bios" command line option.
This can be used for example to load U-Boot images for the
MCF5208EVB (we still lack some features in the CPU emulation for
this firmware, though, so it can not be run successfully yet).

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Thomas Huth <huth@tuxfamily.org>