arm64: zynqmp: Add gpio labels for modepin gpio

Using label helps with better chip identification.
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/12b2fcd94e528c8ca7117f6741aae36b5942b430.1683034376.git.michal.simek@amd.com

arch/arm64/boot/dts/xilinx/zynqmp-sm-k26-revA.dts

@@ -77,6 +77,10 @@ ds36-led {
 	};
 };
 
+&modepin_gpio {
+	label = "modepin";
+};
+
 &uart1 { /* MIO36/MIO37 */
 	status = "okay";
 };