mfd: ac100: Add device tree bindings for X-Powers AC100 codec/RTC combo IC

The AC100 is a multifunction device with an audio codec subsystem and
an RTC subsystem. These two subsystems share a common register space
and host interface.
Signed-off-by: NChen-Yu Tsai <wens@csie.org>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NLee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/mfd/ac100.txt

+X-Powers AC100 Codec/RTC IC Device Tree bindings
+
+AC100 is a audio codec and RTC subsystem combo IC. The 2 parts are
+separated, including power supplies and interrupt lines, but share
+a common register address space and host interface.
+
+Required properties:
+- compatible: "x-powers,ac100"
+- reg: The I2C slave address or RSB hardware address for the chip
+- sub-nodes:
+  - codec
+    - compatible:		"x-powers,ac100-codec"
+    - interrupt-parent:		The parent interrupt controller
+    - interrupts:		SoC NMI / GPIO interrupt connected to the
+    				IRQ_AUDIO pin
+    - #clock-cells:		Shall be 0
+    - clock-output-names:	"4M_adda"
+
+    - see clock/clock-bindings.txt for common clock bindings
+
+  - rtc
+    - compatible:		"x-powers,ac100-rtc"
+    - interrupt-parent:		The parent interrupt controller
+    - interrupts:		SoC NMI / GPIO interrupt connected to the
+    				IRQ_RTC pin
+    - clocks:			A phandle to the codec's "4M_adda" clock
+    - #clock-cells:		Shall be 1
+    - clock-output-names:	"cko1_rtc", "cko2_rtc", "cko3_rtc"
+
+    - see clock/clock-bindings.txt for common clock bindings
+
+Example:
+
+ac100: codec@e89 {
+	compatible = "x-powers,ac100";
+	reg = <0xe89>;
+
+	ac100_codec: codec {
+		compatible = "x-powers,ac100-codec";
+		interrupt-parent = <&r_pio>;
+		interrupts = <0 9 IRQ_TYPE_LEVEL_LOW>; /* PL9 */
+		#clock-cells = <0>;
+		clock-output-names = "4M_adda";
+	};
+
+	ac100_rtc: rtc {
+		compatible = "x-powers,ac100-rtc";
+		interrupt-parent = <&nmi_intc>;
+		interrupts = <0 IRQ_TYPE_LEVEL_LOW>;
+		clocks = <&ac100_codec>;
+		#clock-cells = <1>;
+		clock-output-names = "cko1_rtc", "cko2_rtc", "cko3_rtc";
+	};
+};