hw/misc/iotkit-sysinfo: Implement IoTKit system information block

Implement the IoTKit system control element's system information
block; this is just a pair of read-only version/config registers,
plus the usual PID/CID ID registers.

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: 20180820141116.9118-10-peter.maydell@linaro.org