mpc8544_guts: Fix MemoryRegion name

6544 -> 8544

Signed-off-by: Andreas Färber <afaerber@suse.de>
mpc8544_guts: QOM'ify

Introduce type constant and cast macro.

Signed-off-by: Andreas Färber <afaerber@suse.de>
mpc8544_guts: Convert to QOM realize

Signed-off-by: Andreas Färber <afaerber@suse.de>