kukui: Fix power leakage in LED.
kukui: Fix power leakage in LED.

Though setting the LED brighness to 0, LEDs are still sinking
power.  This causes power leakage (2mA) in G3 state.
This CL turns off the LED current sinking if the LED brightness is set
to 0.  This also fixes LED not able to enter auto mode if it has been
turned off previously.

BRANCH=None
BUG=b:131122365 b:131372801
TEST=see that the gap of the power of batt and sys are reduce from 2mA
     to 0.06mA.
dut-control ppvar_batt_ma ppvar_sys_ma  -t 3 |grep @@
@@            NAME  COUNT  AVERAGE  STDDEV    MAX   MIN
@@    sample_msecs    527     5.69    1.12  11.73  4.73
@@   ppvar_batt_ma    527     3.96    0.29   4.00  2.00
@@    ppvar_sys_ma    527     3.90    0.45   6.00  2.00
TEST=ectool led battery off;
     ectool led battery auto;
     and see the battery led can blink.

Change-Id: I8422eb651781386caa0600448bde3a0825d65ec3
Signed-off-by: Yilun Lin <2f2733c7206ea2b76bd2db1905cc5e8a75841c48@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1588302
Commit-Ready: ChromeOS CL Exonerator Bot <fa429e5907f00867f797423aea74327bb02c91b6@appspot.gserviceaccount.com>
Tested-by: Yilun Lin <2f2733c7206ea2b76bd2db1905cc5e8a75841c48@chromium.org>
Reviewed-by: Nicolas Boichat <f3daba1cdc403799935674d3cd4b0e5bd1804232@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec