dt-bindings: Add devicetree bindings

Add snapshot of device tree bindings from keystone common kernel, branch
"android-mainline-keystone-qcom-release" at c4c12103f9c0 ("Snap for 9228065
from e32903b9a63bb558df8b803b076619c53c16baad to
android-mainline-keystone-qcom-release").

Change-Id: I7682079615cbd9f29340a5c1f2a1d84ec441a1f1
Signed-off-by: Melody Olvera <quic_molvera@quicinc.com>

bindings/mailbox/altera-mailbox.txt

@@ -0,0 +1,48 @@
+Altera Mailbox Driver
+=====================
+
+Required properties:
+- compatible :	"altr,mailbox-1.0".
+- reg : 	physical base address of the mailbox and length of
+		memory mapped region.
+- #mbox-cells:	Common mailbox binding property to identify the number
+		of cells required for the mailbox specifier. Should be 1.
+
+Optional properties:
+- interrupts :		interrupt number. The interrupt specifier format
+			depends on the interrupt controller parent.
+
+Example:
+	mbox_tx: mailbox@100 {
+		compatible = "altr,mailbox-1.0";
+		reg = <0x100 0x8>;
+		interrupt-parent = < &gic_0 >;
+		interrupts = <5>;
+		#mbox-cells = <1>;
+	};
+
+	mbox_rx: mailbox@200 {
+		compatible = "altr,mailbox-1.0";
+		reg = <0x200 0x8>;
+		interrupt-parent = < &gic_0 >;
+		interrupts = <6>;
+		#mbox-cells = <1>;
+	};
+
+Mailbox client
+===============
+"mboxes" and the optional "mbox-names" (please see
+Documentation/devicetree/bindings/mailbox/mailbox.txt for details). Each value
+of the mboxes property should contain a phandle to the mailbox controller
+device node and second argument is the channel index. It must be 0 (hardware
+support only one channel).The equivalent "mbox-names" property value can be
+used to give a name to the communication channel to be used by the client user.
+
+Example:
+	mclient0: mclient0@400 {
+		compatible = "client-1.0";
+		reg = <0x400 0x10>;
+		mbox-names = "mbox-tx", "mbox-rx";
+		mboxes = <&mbox_tx 0>,
+			 <&mbox_rx 0>;
+	};