avocado, risc-v: add tuxboot tests for 'max' CPU

avocado, risc-v: add tuxboot tests for 'max' CPU

Add smoke tests to ensure that we'll not break the 'max' CPU type when
adding new frozen/ratified RISC-V extensions.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20230912132423.268494-12-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>