arm64: dts: microchip: sparx5: do not use PSCI on reference boards

PSCI is not implemented on SparX-5 at all, there is no ATF and U-boot that
is shipped does not implement it as well.

I have tried flashing the latest BSP 2022.12 U-boot which did not work.
After contacting Microchip, they confirmed that there is no ATF for the
SoC nor PSCI implementation which is unfortunate in 2023.

So, disable PSCI as otherwise kernel crashes as soon as it tries probing
PSCI with, and the crash is only visible if earlycon is used.

Since PSCI is not implemented, switch core bringup to use spin-tables
which are implemented in the vendor U-boot and actually work.

Tested on PCB134 with eMMC (VSC5640EV).

Fixes: 6694aee00a ("arm64: dts: sparx5: Add basic cpu support")
Signed-off-by: Robert Marko <robert.marko@sartura.hr>
Acked-by: Steen Hegelund <Steen.Hegelund@microchip.com>
Link: https://lore.kernel.org/r/20230221105039.316819-1-robert.marko@sartura.hr
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

arch/arm64/boot/dts/microchip/sparx5.dtsi

@@ -63,7 +63,7 @@
 		interrupt-affinity = <&cpu0>, <&cpu1>;
 	};
 
-	psci {
+	psci: psci {
 		compatible = "arm,psci-0.2";
 		method = "smc";
 	};

arch/arm64/boot/dts/microchip/sparx5_pcb_common.dtsi

@@ -6,6 +6,18 @@
 /dts-v1/;
 #include "sparx5.dtsi"
 
+&psci {
+	status = "disabled";
+};
+
+&cpu0 {
+	enable-method = "spin-table";
+};
+
+&cpu1 {
+	enable-method = "spin-table";
+};
+
 &uart0 {
 	status = "okay";
 };