arm64: dts: Fix leftover entry-methods for PSCI

These two device trees were either missed or added after
the commit correcting the "entry-method" from
"arm,psci" to just "psci" as per the binding.

Link: https://lore.kernel.org/r/20200322115846.16265-1-linus.walleij@linaro.org
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Chunyan Zhang <chunyan.zhang@unisoc.com>
Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm64/boot/dts/freescale/fsl-ls1028a.dtsi

@@ -53,7 +53,7 @@ idle-states {
 		 * PSCI node is not added default, U-boot will add missing
 		 * parts if it determines to use PSCI.
 		 */
-		entry-method = "arm,psci";
+		entry-method = "psci";
 
 		CPU_PW20: cpu-pw20 {
 			  compatible = "arm,idle-state";

arch/arm64/boot/dts/sprd/sc9863a.dtsi

@@ -108,7 +108,7 @@ CPU7: cpu@700 {
 	};
 
 	idle-states {
-		entry-method = "arm,psci";
+		entry-method = "psci";
 		CORE_PD: core-pd {
 			compatible = "arm,idle-state";
 			entry-latency-us = <4000>;