ARM: dts: NSP: Move USB3 PHY to internal MDIO bus

This patch largely replicates Vivek Unune's patch "ARM: dts:
BCM5301X:Make usb3 phy use mdio phy driver"[1] for the NSP platform,
whereby we need to create an mdio-mux to facilitate switches
configured via external MDIO, in this case on the Meraki MX65.

However in doing so, we are creating an overlap with usb3_phy's
ccb-mii range. To resolve this, usb3_phy should be moved to a child
node of the internal MDIO bus. The result is heavily based upon Vivek's
patch. This has also been cross-referenced with Yendapally Reddy's
earlier work which utilised the subsequently dropped brcm,nsp-usb3-phy
driver: "[PATCH v2 4/4] arm: dts: nsp: Add USB nodes to device tree"
[2]. Finally, this change provides conformance to the bcm-ns-usb3-phy
documentation, utilising the required usb3-dmp-syscon property. Note
that support for the deprecated ccb-mii bindings has been dropped as of
"phy: phy-bcm-ns-usb3: drop support for deprecated DT binding"[3].

[1] https://lore.kernel.org/patchwork/patch/933971/
[2] https://www.spinics.net/lists/arm-kernel/msg555132.html
[3] https://lore.kernel.org/linux-devicetree/[e-mail]/

Signed-off-by: Matthew Hagan <[e-mail]>
Signed-off-by: Florian Fainelli <[e-mail]>

arch/arm/boot/dts/bcm-nsp.dtsi

···
 			#address-cells = <1>;
 		};
 
+		mdio-mux@32000 {
+			compatible = "mdio-mux-mmioreg";
+			reg = <0x32000 0x4>;
+			mux-mask = <0x200>;
+			#address-cells = <1>;
+			#size-cells = <0>;
+			mdio-parent-bus = <&mdio>;
+
+			mdio_int: mdio@0 {
+				reg = <0x0>;
+				#address-cells = <1>;
+				#size-cells = <0>;
+
+				usb3_phy: usb3-phy@10 {
+					compatible = "brcm,ns-bx-usb3-phy";
+					reg = <0x10>;
+					usb3-dmp-syscon = <&usb3_dmp>;
+					#phy-cells = <0>;
+					status = "disabled";
+				};
+			};
+
+			mdio_ext: mdio@200 {
+				reg = <0x200>;
+				#address-cells = <1>;
+				#size-cells = <0>;
+			};
+		};
+
 		rng: rng@33000 {
 			compatible = "brcm,bcm-nsp-rng";
 			reg = <0x33000 0x14>;
···
 			};
 		};
 
-		usb3_phy: usb3-phy@104000 {
-			compatible = "brcm,ns-bx-usb3-phy";
-			reg = <0x104000 0x1000>,
-			      <0x032000 0x1000>;
-			reg-names = "dmp", "ccb-mii";
-			#phy-cells = <0>;
-			status = "disabled";
+		usb3_dmp: syscon@104000 {
+			reg = <0x104000 0x1000>;
 		};
 	};