Add reset option for fan_ctrl interfaces.

For example:
User can use the "echo r > acoustic_limit_rpm_threshold" command
to reset acoustic_limit_rpm_threshold to boot value
Signed-off-by: Ma Jun <Jun.Ma2@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>