[SCSI] Documentation/devicetree: Add DT bindings for UFS host controller

Compatible list is used in commit 03b1781a but is not documented.
Add necessary device tree bindings to describe on-chip UFS host
controllers.
Signed-off-by: NSujit Reddy Thumma <sthumma@codeaurora.org>
Signed-off-by: NSantosh Y <santoshsy@gmail.com>
Signed-off-by: NJames Bottomley <JBottomley@Parallels.com>

Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt

+* Universal Flash Storage (UFS) Host Controller
+
+UFSHC nodes are defined to describe on-chip UFS host controllers.
+Each UFS controller instance should have its own node.
+
+Required properties:
+- compatible        : compatible list, contains "jedec,ufs-1.1"
+- interrupts        : <interrupt mapping for UFS host controller IRQ>
+- reg               : <registers mapping>
+
+Example:
+	ufshc@0xfc598000 {
+		compatible = "jedec,ufs-1.1";
+		reg = <0xfc598000 0x800>;
+		interrupts = <0 28 0>;
+	};