hw/riscv/opentitan: Add TYPE_OPENTITAN_MACHINE definition

QOM type names are usually defined as TYPE_FOO.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-Id: <20230520054510.68822-4-philmd@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

include/hw/riscv/opentitan.h

@@ -53,6 +53,8 @@ struct LowRISCIbexSoCState {
     MemoryRegion flash_alias;
 };
 
+#define TYPE_OPENTITAN_MACHINE "opentitan"
+
 typedef struct OpenTitanState {
     /*< private >*/
     SysBusDevice parent_obj;