ARM: dts: at91: sama5d4_xplained: Remove spi0 node

sama5d4_xplained has an optional on-board serial DataFlash (AT25DF321A),
which does not come populated on board by default. Since the spi0 node
does not have any child populated by default, thus no user on
sama5d4_xplained, remove it. This avoids the following error in SPI NOR,
which reads the values of the pulled downed lines, unrecognizing the flash:

spi-nor spi0.0: unrecognized JEDEC id bytes: 00 00 00 00 00 00
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20210716154739.835738-1-tudor.ambarus@microchip.com

arch/arm/boot/dts/at91-sama5d4_xplained.dts

@@ -38,16 +38,6 @@ uart0: serial@f8004000 {
 				status = "okay";
 			};
 
-			spi0: spi@f8010000 {
-				cs-gpios = <&pioC 3 0>, <0>, <0>, <0>;
-				status = "okay";
-				m25p80@0 {
-					compatible = "atmel,at25df321a";
-					spi-max-frequency = <50000000>;
-					reg = <0>;
-				};
-			};
-
 			i2c0: i2c@f8014000 {
 				i2c-digital-filter;
 				status = "okay";