dt-bindings: mmc: add DT bindings for Milbeaut SD controller

Add the device-tree binding documentation for Milbeaut SDHCI driver.
Signed-off-by: Takao Orito <orito.takao@socionext.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/sdhci-milbeaut.txt

+* SOCIONEXT Milbeaut SDHCI controller
+
+This file documents differences between the core properties in mmc.txt
+and the properties used by the sdhci_milbeaut driver.
+
+Required properties:
+- compatible: "socionext,milbeaut-m10v-sdhci-3.0"
+- clocks: Must contain an entry for each entry in clock-names. It is a
+  list of phandles and clock-specifier pairs.
+  See ../clocks/clock-bindings.txt for details.
+- clock-names: Should contain the following two entries:
+	"iface" - clock used for sdhci interface
+	"core"  - core clock for sdhci controller
+
+Optional properties:
+- fujitsu,cmd-dat-delay-select: boolean property indicating that this host
+  requires the CMD_DAT_DELAY control to be enabled.
+
+Example:
+	sdhci3: mmc@1b010000 {
+		compatible = "socionext,milbeaut-m10v-sdhci-3.0";
+		reg = <0x1b010000 0x10000>;
+		interrupts = <0 265 0x4>;
+		voltage-ranges = <3300 3300>;
+		bus-width = <4>;
+		clocks = <&clk 7>, <&ahb_clk>;
+		clock-names = "core", "iface";
+		cap-sdio-irq;
+		fujitsu,cmd-dat-delay-select;
+	};