arm: dts: armada-cp110-*dtsi: add xmdio nodes

Based on upstream-linux
See https://github.com/torvalds/linux/commit/f66b2aff.

However made the XSMI register window 0x16 (22) bytes per my reading
of the functional spec.  Similar commits in Marvels own repo bump it
to 0x200 (512) bytes but I did not see the reasoning for that.

https://github.com/MarvellEmbeddedProcessors/u-boot-marvell/commit/4d932b4.

Also added device-name attributes to prevent ambiguity in the `mdio`
command.

Signed-off-by: Nevo Hed <nhed+github@starry.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/arch/arm/dts/armada-cp110-slave.dtsi b/arch/arm/dts/armada-cp110-slave.dtsi
index 2fbd7b5..b426a4e 100644
--- a/arch/arm/dts/armada-cp110-slave.dtsi
+++ b/arch/arm/dts/armada-cp110-slave.dtsi
@@ -99,6 +99,15 @@
 				device-name = "cps-mdio";
 			};
 
+			cps_xmdio: mdio@12a600 {
+				#address-cells = <1>;
+				#size-cells = <0>;
+				compatible = "marvell,xmdio";
+				reg = <0x12a600 0x16>;
+				status = "disabled";
+				device-name = "cps-xmdio";
+			};
+
 			cps_syscon0: system-controller@440000 {
 				compatible = "marvell,cp110-system-controller0",
 					     "syscon";