dt-bindings: Add SLIMbus bindings

SLIMbus (Serial Low Power Interchip Media Bus) is a specification
developed by MIPI (Mobile Industry Processor Interface) alliance.
SLIMbus is a 2-wire implementation, which is used to communicate with
peripheral components like audio-codec.

This patch adds device tree bindings for the slimbus.
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviwed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/slimbus/bus.txt

+SLIM(Serial Low Power Interchip Media Bus) bus
+
+SLIMbus is a 2-wire bus, and is used to communicate with peripheral
+components like audio-codec.
+
+Required property for SLIMbus controller node:
+- compatible	- name of SLIMbus controller
+
+Child nodes:
+Every SLIMbus controller node can contain zero or more child nodes
+representing slave devices on the bus. Every SLIMbus slave device is
+uniquely determined by the enumeration address containing 4 fields:
+Manufacturer ID, Product code, Device index, and Instance value for
+the device.
+If child node is not present and it is instantiated after device
+discovery (slave device reporting itself present).
+
+In some cases it may be necessary to describe non-probeable device
+details such as non-standard ways of powering up a device. In
+such cases, child nodes for those devices will be present as
+slaves of the SLIMbus controller, as detailed below.
+
+Required property for SLIMbus child node if it is present:
+- reg		- Should be ('Device index', 'Instance ID') from SLIMbus
+		  Enumeration  Address.
+		  Device Index Uniquely identifies multiple Devices within
+		  a single Component.
+		  Instance ID Is for the cases where multiple Devices of the
+		  same type or Class are attached to the bus.
+
+- compatible	-"slimMID,PID". The textual representation of Manufacturer ID,
+	 	  Product Code, shall be in lower case hexadecimal with leading
+		  zeroes suppressed
+
+SLIMbus example for Qualcomm's slimbus manager component:
+
+	slim@28080000 {
+		compatible = "qcom,apq8064-slim", "qcom,slim";
+		reg = <0x28080000 0x2000>,
+		interrupts = <0 33 0>;
+		clocks = <&lcc SLIMBUS_SRC>, <&lcc AUDIO_SLIMBUS_CLK>;
+		clock-names = "iface", "core";
+		#address-cells = <2>;
+		#size-cell = <0>;
+
+		codec: wcd9310@1,0{
+			compatible = "slim217,60";
+			reg = <1 0>;
+		};
+	};