target/nios2: Convert to 3-phase reset

target/nios2: Convert to 3-phase reset

Convert the nios2 CPU class to use 3-phase reset, so it doesn't
need to use device_class_set_parent_reset() any more.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Edgar E. Iglesias <edgar@zeroasic.com>
Reviewed-by: Taylor Simpson <tsimpson@quicinc.com>
Message-id: 20221124115023.2437291-12-peter.maydell@linaro.org