hw/arm/armsse: Make SSE-300 use Cortex-M55

The SSE-300 has a Cortex-M55 (which was the whole reason for us
modelling it), but we forgot to actually update the code to let it
have a different CPU type from the IoTKit and SSE-200.  Add CPU type
as a field for ARMSSEInfo instead of hardcoding it to always use a
Cortex-M33.

Buglink: https://bugs.launchpad.net/qemu/+bug/1923861


Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210416104010.13228-1-peter.maydell@linaro.org