ARC: [plat-axs10x]: PGU: remove unused encoder-slave property

ARC PGU is looking for encoder via endpoint mechanism and doesn't
use "encoder-slave" property for a long time. Let's drop unused
"encoder-slave" property from ARC PGU node in axs10x.
Acked-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/boot/dts/axs10x_mb.dtsi

@@ -305,7 +305,6 @@ gpio1_bankc: gpio-controller@2 {
 		pgu@17000 {
 			compatible = "snps,arcpgu";
 			reg = <0x17000 0x400>;
-			encoder-slave = <&adv7511>;
 			clocks = <&pguclk>;
 			clock-names = "pxlclk";
 			memory-region = <&frame_buffer>;