ACPI: thinkpad-acpi: attempt to preserve fan state on resume

ACPI: thinkpad-acpi: attempt to preserve fan state on resume

Attempt to preserve fan state across sleep and hibernation if the fan
control mode is enabled.

For safety reasons, only the PWM OFF (fan at 100%) or maximum
closed-loop level (level 7) are preserved.  If the fan state was set
to anything else, it will not be restored.

Also, should the fan be at PWM OFF mode at resume, it will be left at
that state (but this is extremely unlikely, no ThinkPad firmware was
ever reported to do this).

For reference, the known states used for fan control upon resume by
the firmware  are either "auto" or "level 7" depending on whether the
laptop wakes due to normal conditions or a thermal emergency.

Fixes: http://bugzilla.kernel.org/show_bug.cgi?id=11331

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Richard Hartmann <richih.mailinglist@gmail.com>