mmc: sdhci-spear: add device tree bindings

This adds simple DT bindings for SDHCI SPEAr controller. It uses cd-gpios
from common mmc bindings.

This also fixes spear300-evb.dts with correct name for card detect binding.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

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

@@ -0,0 +1,21 @@
+* SPEAr SDHCI Controller
+
+This file documents differences between the core properties in mmc.txt
+and the properties used by the sdhci-spear driver.
+
+Required properties:
+- compatible: "st,spear300-sdhci"
+
+Optional properties:
+- cd-gpios: card detect gpio, with zero flags.
+
+If your board don't support these gpios then don't pass the entry.
+
+Example:
+
+	sdhci@fc000000 {
+		compatible = "st,spear300-sdhci";
+		reg = <0xfc000000 0x1000>;
+
+		cd-gpios = <&gpio0 6 0>
+	};