driver: reset: sti: add keyscan for stih416

Add keyscan reset on stih416 reset controller.

Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Giuseppe Condorelli <giuseppe.condorelli@st.com>
Signed-off-by: Gabriel Fernandez <gabriel.fernandez@linaro.org>
Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>