hw/arm: Display CPU type in machine description

Most of ARM machines display their CPU when QEMU list the available
machines (-M help). Some machines do not. Fix to unify the help
output.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20210131184449.382425-7-f4bug@amsat.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/arm/netduino2.c

@@ -54,7 +54,7 @@ static void netduino2_init(MachineState *machine)
 
 static void netduino2_machine_init(MachineClass *mc)
 {
-    mc->desc = "Netduino 2 Machine";
+    mc->desc = "Netduino 2 Machine (Cortex-M3)";
     mc->init = netduino2_init;
     mc->ignore_memory_transaction_failures = true;
 }