Documentation: dt-bindings: minimal documentation for MVEBU SDRAM controller

The suspend/resume code for Armada XP has to modify certain registers
of the SDRAM controller. Therefore, we need to define a Device Tree
binding for this hardware block.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: devicetree@vger.kernel.org
Cc: Kumar Gala <galak@codeaurora.org>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Rob Herring <robh+dt@kernel.org>
Reviewed-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Link: https://lkml.kernel.org/r/1416585613-2113-2-git-send-email-thomas.petazzoni@free-electrons.comSigned-off-by: Jason Cooper <jason@lakedaemon.net>

Documentation/devicetree/bindings/memory-controllers/mvebu-sdram-controller.txt

+Device Tree bindings for MVEBU SDRAM controllers
+
+The Marvell EBU SoCs all have a SDRAM controller. The SDRAM controller
+differs from one SoC variant to another, but they also share a number
+of commonalities.
+
+For now, this Device Tree binding documentation only documents the
+Armada XP SDRAM controller.
+
+Required properties:
+
+ - compatible: for Armada XP, "marvell,armada-xp-sdram-controller"
+ - reg: a resource specifier for the register space, which should
+   include all SDRAM controller registers as per the datasheet.
+
+Example:
+
+sdramc@1400 {
+	compatible = "marvell,armada-xp-sdram-controller";
+	reg = <0x1400 0x500>;
+};