dt-bindings: Add binding for brcm,bcm2835-sdhost.

This is the other SD controller on the platform, which can be swapped
to the role of SD card host using pin muxing.
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/brcm,bcm2835-sdhost.txt

+Broadcom BCM2835 SDHOST controller
+
+This file documents differences between the core properties described
+by mmc.txt and the properties that represent the BCM2835 controller.
+
+Required properties:
+- compatible: Should be "brcm,bcm2835-sdhost".
+- clocks: The clock feeding the SDHOST controller.
+
+Optional properties:
+- dmas: DMA channel for read and write.
+          See Documentation/devicetree/bindings/dma/dma.txt for details
+
+Example:
+
+sdhost: mmc@7e202000 {
+	compatible = "brcm,bcm2835-sdhost";
+	reg = <0x7e202000 0x100>;
+	interrupts = <2 24>;
+	clocks = <&clocks BCM2835_CLOCK_VPU>;
+	dmas = <&dma 13>;
+	dma-names = "rx-tx";
+};