arm64: dts: ls1028a: support external trigger timestamp fifo of PTP timer

There is an external trigger timestamp fifo for PTP timer
of LS1028A. Add property fsl,extts-fifo for that.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/fsl-ls1028a.dtsi

@@ -722,6 +722,7 @@
 				reg = <0x000400 0 0 0 0>;
 				clocks = <&clockgen 4 0>;
 				little-endian;
+				fsl,extts-fifo;
 			};
 		};
 	};