dt-bindings: rtc: add bindings for FlexTimer Module

The patch adds bindings for FlexTimer Module
Signed-off-by: Biwen Li <biwen.li@nxp.com>
Link: https://lore.kernel.org/r/20190813030157.48590-2-biwen.li@nxp.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Documentation/devicetree/bindings/rtc/rtc-fsl-ftm-alarm.txt

+Freescale FlexTimer Module (FTM) Alarm
+
+Required properties:
+- compatible : Should be "fsl,<chip>-ftm-alarm", the
+	       supported chips include
+	       "fsl,ls1012a-ftm-alarm"
+	       "fsl,ls1021a-ftm-alarm"
+	       "fsl,ls1028a-ftm-alarm"
+	       "fsl,ls1043a-ftm-alarm"
+	       "fsl,ls1046a-ftm-alarm"
+	       "fsl,ls1088a-ftm-alarm"
+	       "fsl,ls208xa-ftm-alarm"
+	       "fsl,lx2160a-ftm-alarm"
+- reg : Specifies base physical address and size of the register sets for the
+  FlexTimer Module.
+- interrupts : Should be the FlexTimer Module interrupt.
+- fsl,rcpm-wakeup property and rcpm node : Please refer
+	Documentation/devicetree/bindings/soc/fsl/rcpm.txt
+
+Optional properties:
+- big-endian: If the host controller is big-endian mode, specify this property.
+  The default endian mode is little-endian.
+
+Example:
+rcpm: rcpm@1e34040 {
+	compatible = "fsl,ls1088a-rcpm", "fsl,qoriq-rcpm-2.1+";
+	reg = <0x0 0x1e34040 0x0 0x18>;
+	#fsl,rcpm-wakeup-cells = <6>;
+};
+
+ftm_alarm0: timer@2800000 {
+	compatible = "fsl,ls1088a-ftm-alarm";
+	reg = <0x0 0x2800000 0x0 0x10000>;
+	fsl,rcpm-wakeup = <&rcpm 0x0 0x0 0x0 0x0 0x4000 0x0>;
+	interrupts = <0 44 4>;
+};