power: reset: st: Provide DT bindings for ST's Power Reset driver

Signed-off-by: NChristophe Kerello <christophe.kerello@st.com>
Signed-off-by: NLee Jones <lee.jones@linaro.org>
Signed-off-by: NSebastian Reichel <sre@kernel.org>

Documentation/devicetree/bindings/power/reset/st-reset.txt

+*Device-Tree bindings for ST SW reset functionality
+
+Required properties:
+- compatible: should be "st,<chip>-restart".
+- st,syscfg: should be a phandle of the syscfg node.
+
+Example node:
+	restart {
+		compatible = "st,stih416-restart";
+		st,syscfg = <&syscfg_sbc>;
+	};