e1000e: Add support for S0ix

e1000e: Add support for S0ix

Implement flow for S0ix support. Modern SoCs support S0ix low power
states during idle periods, which are sub-states of ACPI S0 that increase
power saving while supporting an instant-on experience for providing
lower latency that ACPI S0. The S0ix states shut off parts of the SoC
when they are not in use, while still maintaning optimal performance.
This patch add support for S0ix started from an Ice Lake platform.

Suggested-by: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Signed-off-by: Vitaly Lifshits <vitaly.lifshits@intel.com>
Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@linux.intel.com>
Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>