dt-bindings: mmc: add DT binding for S3C24XX MMC/SD/SDIO controller

Adds the device tree bindings description for Samsung S3C24XX
MMC/SD/SDIO controller, used as a connectivity interface with external
MMC, SD and SDIO storage mediums.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sergio Prado <sergio.prado@e-labworks.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/samsung,s3cmci.txt

+* Samsung's S3C24XX MMC/SD/SDIO controller device tree bindings
+
+Samsung's S3C24XX MMC/SD/SDIO controller is used as a connectivity interface
+with external MMC, SD and SDIO storage mediums.
+
+This file documents differences between the core mmc properties described by
+mmc.txt and the properties used by the Samsung S3C24XX MMC/SD/SDIO controller
+implementation.
+
+Required SoC Specific Properties:
+- compatible: should be one of the following
+  - "samsung,s3c2410-sdi": for controllers compatible with s3c2410
+  - "samsung,s3c2412-sdi": for controllers compatible with s3c2412
+  - "samsung,s3c2440-sdi": for controllers compatible with s3c2440
+- reg: register location and length
+- interrupts: mmc controller interrupt
+- clocks: Should reference the controller clock
+- clock-names: Should contain "sdi"
+
+Required Board Specific Properties:
+- pinctrl-0: Should specify pin control groups used for this controller.
+- pinctrl-names: Should contain only one value - "default".
+
+Optional Properties:
+- bus-width: number of data lines (see mmc.txt)
+- cd-gpios: gpio for card detection (see mmc.txt)
+- wp-gpios: gpio for write protection (see mmc.txt)
+
+Example:
+
+	mmc0: mmc@5a000000 {
+		compatible = "samsung,s3c2440-sdi";
+		pinctrl-names = "default";
+		pinctrl-0 = <&sdi_pins>;
+		reg = <0x5a000000 0x100000>;
+		interrupts = <0 0 21 3>;
+		clocks = <&clocks PCLK_SDI>;
+		clock-names = "sdi";
+		bus-width = <4>;
+		cd-gpios = <&gpg 8 GPIO_ACTIVE_LOW>;
+		wp-gpios = <&gph 8 GPIO_ACTIVE_LOW>;
+	};