hw/riscv/opentitan: Declare QOM types using DEFINE_TYPES() macro

hw/riscv/opentitan: Declare QOM types using DEFINE_TYPES() macro

When multiple QOM types are registered in the same file,
it is simpler to use the the DEFINE_TYPES() macro. Replace
the type_init() / type_register_static() combination. This
is in preparation of adding the OpenTitan machine type to
this array in a pair of commits.

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: <20230520054510.68822-3-philmd@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>