dt-bindings: Add bindings for Broadcom STB DRAM Sensors

Provide bindings for the Broadcom STB DDR PHY Front End (DPFE).
Signed-off-by: NMarkus Mayer <mmayer@broadcom.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NFlorian Fainelli <f.fainelli@gmail.com>

Documentation/devicetree/bindings/memory-controllers/brcm,dpfe-cpu.txt

+DDR PHY Front End (DPFE) for Broadcom STB
+=========================================
+
+DPFE and the DPFE firmware provide an interface for the host CPU to
+communicate with the DCPU, which resides inside the DDR PHY.
+
+There are three memory regions for interacting with the DCPU. These are
+specified in a single reg property.
+
+Required properties:
+  - compatible: must be "brcm,bcm7271-dpfe-cpu", "brcm,bcm7268-dpfe-cpu"
+    or "brcm,dpfe-cpu"
+  - reg: must reference three register ranges
+      - start address and length of the DCPU register space
+      - start address and length of the DCPU data memory space
+      - start address and length of the DCPU instruction memory space
+  - reg-names: must contain "dpfe-cpu", "dpfe-dmem", and "dpfe-imem";
+        they must be in the same order as the register declarations
+
+Example:
+	dpfe_cpu0: dpfe-cpu@f1132000 {
+		compatible = "brcm,bcm7271-dpfe-cpu", "brcm,dpfe-cpu";
+		reg =  <0xf1132000 0x180
+			0xf1134000 0x1000
+			0xf1138000 0x4000>;
+		reg-names = "dpfe-cpu", "dpfe-dmem", "dpfe-imem";
+	};