arm64: dts: microchip: sparx5_pcb135: drop duplicated NOR flash

Since beginning the DTS extended the SPI0 in two places adding two SPI
muxes, each with same SPI NOR flash.  Both used exactly the same
chip-selects, so this was clearly buggy code.  Then in commit
d0f482bb ("arm64: dts: sparx5: Add the Sparx5 switch node") one SPI
mux was removed, while keeping the SPI NOR flash node.

This still leaves duplicated SPI nodes under same chip select 0,
reported by dtc W=1 warnings:

  sparx5_pcb135_board.dtsi:92.10-96.4: Warning (unique_unit_address_if_enabled): /axi@600000000/spi@600104000/flash@0: duplicate unit-address (also used in node /axi@600000000/spi@600104000/spi@0)

Steen Hegelund confirmed that in fact there is a SPI mux, thus remove
the duplicated node without the mux.
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Tested-by: Steen Hegelund <Steen.Hegelund@microchip.com>
Reviewed-by: Steen Hegelund <Steen.Hegelund@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

arch/arm64/boot/dts/microchip/sparx5_pcb135_board.dtsi

@@ -87,15 +87,6 @@ i2cmux_s32: i2cmux-3-pins {
 	};
 };
 
-&spi0 {
-	status = "okay";
-	flash@0 {
-		compatible = "jedec,spi-nor";
-		spi-max-frequency = <8000000>;
-		reg = <0>;
-	};
-};
-
 &spi0 {
 	status = "okay";
 	spi@0 {