intel: thermal: PCH: Drop ACPI_FADT_LOW_POWER_S0 check

If ACPI_FADT_LOW_POWER_S0 is not set, this doesn't mean that low-power
S0 idle is not usable.  It merely means that using S3 on the given
system is more beneficial from the energy saving perspective than using
low-power S0 idle, as long as S3 is supported.

Suspend-to-idle is still a valid suspend mode if ACPI_FADT_LOW_POWER_S0
is not set and the pm_suspend_via_firmware() check in pch_wpt_suspend()
is sufficient to distinguish suspend-to-idle from S3, so drop the
confusing ACPI_FADT_LOW_POWER_S0 check.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Zhang Rui <rui.zhang@intel.com>