Embed CPUM68KState as first member of QOM M68kCPU.
Drop cpu_m68k_close() in favor of object_delete().

Let CPUClass::reset() call cpu_state_reset() for now.
Signed-off-by: NAndreas Färber <afaerber@suse.de>
Reviewed-by: NLaurent Vivier <Laurent@Vivier.EU>
Tested-by: NLaurent Vivier <Laurent@Vivier.EU>