fan: Disable fan when duty / RPM is set to zero
fan: Disable fan when duty / RPM is set to zero

BRANCH=master
BUG=none
TEST=Check GPIO(fan_t.enable_gpio) if it is low when S3 or S0ix or
0% duty or 0 RPM on kunimitsu.

Change-Id: I6aecae269fa8bb41a811e75089757fe714576160
Signed-off-by: Kyoung Kim <0fa79f8568f83616b048a28252e7d9ad3c59c80d@intel.com>
Reviewed-on: https://chromium-review.googlesource.com/310391
Commit-Ready: Kyoung Il Kim <0fa79f8568f83616b048a28252e7d9ad3c59c80d@intel.com>
Tested-by: Kyoung Il Kim <0fa79f8568f83616b048a28252e7d9ad3c59c80d@intel.com>
Reviewed-by: Kyoung Il Kim <0fa79f8568f83616b048a28252e7d9ad3c59c80d@intel.com>
Reviewed-by: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>

coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics