powerpc: Document FSL eSDHC bindings

This patch documents OF bindings for the Freescale Enhanced Secure
Digital Host Controller.
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

Documentation/powerpc/dts-bindings/fsl/esdhc.txt

+* Freescale Enhanced Secure Digital Host Controller (eSDHC)
+
+The Enhanced Secure Digital Host Controller provides an interface
+for MMC, SD, and SDIO types of memory cards.
+
+Required properties:
+  - compatible : should be
+    "fsl,<chip>-esdhc", "fsl,mpc8379-esdhc" for MPC83xx processors.
+    "fsl,<chip>-esdhc", "fsl,mpc8536-esdhc" for MPC85xx processors.
+  - reg : should contain eSDHC registers location and length.
+  - interrupts : should contain eSDHC interrupt.
+  - interrupt-parent : interrupt source phandle.
+  - clock-frequency : specifies eSDHC base clock frequency.
+
+Example:
+
+sdhci@2e000 {
+	compatible = "fsl,mpc8378-esdhc", "fsl,mpc8379-esdhc";
+	reg = <0x2e000 0x1000>;
+	interrupts = <42 0x8>;
+	interrupt-parent = <&ipic>;
+	/* Filled in by U-Boot */
+	clock-frequency = <0>;
+};