arm64: tegra: Enable CPU idle support for Shield

Enable CPU idle support for Shield platform.
Signed-off-by: Joseph Lo <josephl@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

arch/arm64/boot/dts/nvidia/tegra210-p2894.dtsi

@@ -1629,6 +1629,12 @@ cpu@2 {
 		cpu@3 {
 			enable-method = "psci";
 		};
+
+		idle-states {
+			cpu-sleep {
+				status = "okay";
+			};
+		};
 	};
 
 	psci {