arm64: dts: allwinner: a523: Add I2S2 pins on PI pin group

The Radxa Cubie A5E exposes I2S2 through the PI pin group on the 40-pin
GPIO header.

Add a pinmux setting for it so potential users can directly reference
it.

Acked-by: Jernej Skrabec <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Chen-Yu Tsai <[e-mail]>

arch/arm64/boot/dts/allwinner/sun55i-a523.dtsi

···
 			interrupt-controller;
 			#interrupt-cells = <3>;
 
+			/omit-if-no-ref/
+			i2s2_pi_pins: i2s2-pi-pins {
+				pins = "PI2", "PI3", "PI4", "PI5";
+				allwinner,pinmux = <5>;
+				function = "i2s2";
+				bias-disable;
+			};
+
 			mmc0_pins: mmc0-pins {
 				pins = "PF0" ,"PF1", "PF2", "PF3", "PF4", "PF5";
 				allwinner,pinmux = <2>;