ARM: dts: DRA7: Add PRUSS MDIO controller nodes

The PRUSSs on AM57xx SoCs contain an MDIO controller that can
be used to control external PHYs associated with the Industrial
Ethernet peripherals within each PRUSS. The MDIO module used
within the PRU-ICSS is an instance of the MDIO Controller used
in TI Davinci SoCs. The same bus frequency of 1 MHz is chosen as
the regular MDIO node.

The nodes are added to the common DRA7 dts file and are disabled.
These need to be enabled in the respective board files supporting
AM57xx SoCs and where the ethernet is pinned out and connected
properly.

Signed-off-by: Andrew F. Davis <afd@ti.com>
[s-anna@ti.com: revise commit description]
Signed-off-by: Suman Anna <s-anna@ti.com>

arch/arm/boot/dts/dra7.dtsi

@@ -1249,6 +1249,17 @@
 					reg-names = "iram", "control", "debug";
 					firmware-name = "am57xx-pru1_1-fw";
 				};
+
+				pruss1_mdio: mdio@4b232400 {
+					compatible = "ti,davinci_mdio";
+					reg = <0x4b232400 0x90>;
+					#address-cells = <1>;
+					#size-cells = <0>;
+					clocks = <&dpll_gmac_h13x2_ck>;
+					clock-names = "fck";
+					bus_freq = <1000000>;
+					status = "disabled";
+				};
 			};
 		};
 
@@ -1327,6 +1338,17 @@
 					reg-names = "iram", "control", "debug";
 					firmware-name = "am57xx-pru2_1-fw";
 				};
+
+				pruss2_mdio: mdio@4b2b2400 {
+					compatible = "ti,davinci_mdio";
+					reg = <0x4b2b2400 0x90>;
+					#address-cells = <1>;
+					#size-cells = <0>;
+					clocks = <&dpll_gmac_h13x2_ck>;
+					clock-names = "fck";
+					bus_freq = <1000000>;
+					status = "disabled";
+				};
 			};
 		};