dt-bindings: pwm-stm32: Document pinctrl sleep state

Add documentation for pinctrl sleep state that can be used by STM32
timers PWM.
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

Documentation/devicetree/bindings/pwm/pwm-stm32.txt

@@ -5,8 +5,9 @@ See ../mfd/stm32-timers.txt for details about the parent node.
 
 Required parameters:
 - compatible:		Must be "st,stm32-pwm".
-- pinctrl-names: 	Set to "default".
-- pinctrl-0: 		List of phandles pointing to pin configuration nodes for PWM module.
+- pinctrl-names: 	Set to "default". An additional "sleep" state can be
+			defined to set pins in sleep state when in low power.
+- pinctrl-n: 		List of phandles pointing to pin configuration nodes for PWM module.
 			For Pinctrl properties see ../pinctrl/pinctrl-bindings.txt
 - #pwm-cells:		Should be set to 3. This PWM chip uses the default 3 cells
 			bindings defined in pwm.txt.
@@ -32,7 +33,8 @@ Example:
 			compatible = "st,stm32-pwm";
 			#pwm-cells = <3>;
 			pinctrl-0	= <&pwm1_pins>;
-			pinctrl-names	= "default";
+			pinctrl-1	= <&pwm1_sleep_pins>;
+			pinctrl-names	= "default", "sleep";
 			st,breakinput = <0 1 5>;
 		};
 	};