arm64: dts: ti: k3-am64-phycore-som: Add serial_flash label

Label the spi nor as serial_flash. This allows us to disable the
flash with an overlay common to all am6xx-phycore-som boards.
Signed-off-by: Nathan Morrisson <nmorrisson@phytec.com>
Link: https://lore.kernel.org/r/20240613230759.1984966-2-nmorrisson@phytec.comSigned-off-by: Vignesh Raghavendra <vigneshr@ti.com>

arch/arm64/boot/dts/ti/k3-am64-phycore-som.dtsi

@@ -340,7 +340,7 @@ &ospi0 {
 	pinctrl-names = "default";
 	pinctrl-0 = <&ospi0_pins_default>;
 
-	flash@0 {
+	serial_flash: flash@0 {
 		compatible = "jedec,spi-nor";
 		reg = <0x0>;
 		spi-tx-bus-width = <8>;