dt-bindings: mfd: Add bindings for STM32 Timers driver

Add bindings information for STM32 Timers

version 6:
- rename stm32-gtimer to stm32-timers
- change compatible
- add description about the IPs

version 2:
- rename stm32-mfd-timer to stm32-gptimer
- only keep one compatible string
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/mfd/stm32-timers.txt

+STM32 Timers driver bindings
+
+This IP provides 3 types of timer along with PWM functionality:
+- advanced-control timers consist of a 16-bit auto-reload counter driven by a programmable
+  prescaler, break input feature, PWM outputs and complementary PWM ouputs channels.
+- general-purpose timers consist of a 16-bit or 32-bit auto-reload counter driven by a
+  programmable prescaler and PWM outputs.
+- basic timers consist of a 16-bit auto-reload counter driven by a programmable prescaler.
+
+Required parameters:
+- compatible: must be "st,stm32-timers"
+
+- reg:			Physical base address and length of the controller's
+			registers.
+- clock-names:		Set to "int".
+- clocks: 		Phandle to the clock used by the timer module.
+			For Clk properties, please refer to ../clock/clock-bindings.txt
+
+Optional parameters:
+- resets:		Phandle to the parent reset controller.
+			See ../reset/st,stm32-rcc.txt
+
+Optional subnodes:
+- pwm:			See ../pwm/pwm-stm32.txt
+- timer:		See ../iio/timer/stm32-timer-trigger.txt
+
+Example:
+	timers@40010000 {
+		#address-cells = <1>;
+		#size-cells = <0>;
+		compatible = "st,stm32-timers";
+		reg = <0x40010000 0x400>;
+		clocks = <&rcc 0 160>;
+		clock-names = "clk_int";
+
+		pwm {
+			compatible = "st,stm32-pwm";
+			pinctrl-0	= <&pwm1_pins>;
+			pinctrl-names	= "default";
+		};
+
+		timer@0 {
+			compatible = "st,stm32-timer-trigger";
+			reg = <0>;
+		};
+	};