hw/misc/iotkit-secctl: Wire up registers for controlling MSCs

hw/misc/iotkit-secctl: Wire up registers for controlling MSCs

The IoTKit does not have any Master Security Contollers itself,
but it does provide registers in the secure privilege control
block which allow control of MSCs in the external system.
Add support for these registers.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180820141116.9118-13-peter.maydell@linaro.org
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>