schedutil governor's DT glue
-----------------------------------------------

This is DT specific glue layer for schedutil governor for sprd systems.

For some SOCs, such as sharkL3, there is no hardware auto scaling for
DVFS under WFI, so, a software slack timer was added in schedutil to
check whether the OPP is the lowest one and scaling to the lowest one
if not.

For some other SOCs with hardware auto scaling for DVFS under WFI, there
is no need to add software slack timer in schedutil.

This property is added to indicate that this SOC need software slack timer
support in schedutil, which help to check the OPP after cpu entered WFI.

Required properties
- sugov_slack_timer
	value type: boolean
	Description: config this property, indicate this SOC need software
	support; else, indicate this SOC no need software support.
	There is no need to add this property into every cpu node, once this
	property is searched in one cpu node, the parsed logic will stop and
	considered this SOC need software support.

Examples:

CPU0: cpu@0 {
	      device_type = "cpu";
	      compatible = "arm,cortex-a55","arm,armv8";
	      reg = <0x0 0x0>;
	      enable-method = "psci";
	      cpu-supply = <&fan53555_dcdc>;
	      cpufreq-data-v1 = <&cpufreq_clus0>;
	      cpu-idle-states = <&CORE_PD>;
	      sched-energy-costs = <&CPU_COST_0 &CLUSTER_COST_0>;
	      capacity-dmips-mhz = <1024>;
	      sugov_slack_timer;
      };

