arm64: zynqmp: Use only earlycon bootargs instead of full one

This is the same patch as was done earlier.
Please look at Linux patch:
"arm64: zynqmp: Use only earlycon bootargs instead of full one"
(sha1: f3609c8d4af28b9cc22ca49bf8e529b582ec188c)

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/arm/dts/zynqmp-zc1751-xm019-dc5.dts

@@ -28,7 +28,7 @@
 	};
 
 	chosen {
-		bootargs = "earlycon=cdns,mmio,0xff000000,115200n8";
+		bootargs = "earlycon";
 		stdout-path = "serial0:115200n8";
 	};