arm64: dts: allwinner: a523: Add SPDIF TX pin on PB and PI pins

The SPDIF TX (called OWA OUT in the datasheet) is available on three
pins. Of those, the PH pin is unlikely to be used since it conflicts
with the first Ethernet controller.

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

The Orange Pi 4A exposes SPDIF TX through both the PB and PI pin
groups on the 40-pin GPIO header. The PB pin alternatively would be
used for I2S0 though.

Add pinmux settings for both options so potential users can directly
reference either one.

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

···
 				bias-disable;
 			};
 
+			/omit-if-no-ref/
+			spdif_out_pb_pin: spdif-pb-pin {
+				pins = "PB8";
+				function = "spdif";
+				allwinner,pinmux = <2>;
+			};
+
+			/omit-if-no-ref/
+			spdif_out_pi_pin: spdif-pi-pin {
+				pins = "PI10";
+				function = "spdif";
+				allwinner,pinmux = <2>;
+			};
+
 			uart0_pb_pins: uart0-pb-pins {
 				pins = "PB9", "PB10";
 				allwinner,pinmux = <2>;