dts: nxp: Add a property to get USB controller type

The property is similar to the usb_controller_index_t
enum that is available in the NXP SDK.

Signed-off-by: Mahesh Mahadevan <mahesh.mahadevan@nxp.com>
diff --git a/dts/arm/nxp/nxp_lpc55S6x_common.dtsi b/dts/arm/nxp/nxp_lpc55S6x_common.dtsi
index 6b9c167..742e11b 100644
--- a/dts/arm/nxp/nxp_lpc55S6x_common.dtsi
+++ b/dts/arm/nxp/nxp_lpc55S6x_common.dtsi
@@ -313,6 +313,7 @@
 		reg = <0x94000 0x1000>;
 		interrupts = <47 1>;
 		num-bidir-endpoints = <5>;
+		usb-controller-index = "LpcIp3511Hs0";
 		status = "disabled";
 	};