Embed CPUMBState as first member of QOM MicroBlazeCPU.

Let CPUClass::reset() call cpu_state_reset() for now.

Signed-off-by: Andreas Färber <afaerber@suse.de>
Tested-by: Peter A. G. Crosthwaite <peter.crosthwaite@petalogix.com>
[AF: Updated cpu.c to include cpu-qom.h indirectly via cpu.h]