Qualcomm GLINK edge binding

This binding describes a Qualcomm GLINK edge, a fifo based mechanism for
communication between subsystem-pairs on various Qualcomm platforms. Two types
of edges can be described by the binding; the GLINK RPM edge and a SMEM based
edge.

- compatible:
	Usage: required for glink-rpm
	Value type: <stringlist>
	Definition: must be "qcom,glink-rpm"

- label:
	Usage: optional
	Value type: <string>
	Definition: should specify the subsystem name this edge corresponds to.

- interrupts:
	Usage: required
	Value type: <prop-encoded-array>
	Definition: should specify the IRQ used by the remote processor to
		    signal this processor about communication related events

- qcom,rpm-msg-ram:
	Usage: required for glink-rpm
	Value type: <prop-encoded-array>
	Definition: handle to RPM message memory resource

- mboxes:
	Usage: required
	Value type: <prop-encoded-array>
	Definition: reference to the "rpm_hlos" mailbox in APCS, as described
		    in mailbox/mailbox.txt

= GLINK DEVICES
Each subnode of the GLINK node represent function tied to a virtual
communication channel. The name of the nodes are not important. The properties
of these nodes are defined by the individual bindings for the specific function
- but must contain the following property:

- qcom,glink-channels:
	Usage: required
	Value type: <stringlist>
	Definition: a list of channels tied to this function, used for matching
		    the function to a set of virtual channels

- qcom,intents:
	Usage: optional
	Value type: <prop-encoded-array>
	Definition: a list of size,amount pairs describing what intents should
		    be preallocated for this virtual channel. This can be used
		    to tweak the default intents available for the channel to
		    meet expectations of the remote.

= EXAMPLE
The following example represents the GLINK RPM node on a MSM8996 device, with
the function for the "rpm_request" channel defined, which is used for
regualtors and root clocks.

	apcs_glb: mailbox@9820000 {
		compatible = "qcom,msm8996-apcs-hmss-global";
		reg = <0x9820000 0x1000>;

		#mbox-cells = <1>;
	};

	rpm_msg_ram: memory@68000 {
		compatible = "qcom,rpm-msg-ram";
		reg = <0x68000 0x6000>;
	};

	rpm-glink {
		compatible = "qcom,glink-rpm";

		interrupts = <GIC_SPI 168 IRQ_TYPE_EDGE_RISING>;

		qcom,rpm-msg-ram = <&rpm_msg_ram>;

		mboxes = <&apcs_glb 0>;

		rpm-requests {
			compatible = "qcom,rpm-msm8996";
			qcom,glink-channels = "rpm_requests";

			qcom,intents = <0x400 5
					0x800 1>;
			...
		};
	};