reef: add power led behavior
reef: add power led behavior

There is only one set LED in reef, so with charger attached, LED behave as
charging LED; without charger, as power LED.

BUG=chrome-os-partner:55492
BRANCH=none
TEST=on reef proto, verified power led behavior is correct in s0/s3/g3

Change-Id: If6b83c46fc4b8b455531698177f559ca319d241a
Signed-off-by: li feng <0fd15d95d647a38d004d7ac9a3d0587bb1c98551@intel.com>
Reviewed-on: https://chromium-review.googlesource.com/366102
Commit-Ready: Kevin K Wong <8bf1d1ccd36a6bfde85ceaaa1fe52f2093ecf3aa@intel.com>
Tested-by: Li1 Feng <0fd15d95d647a38d004d7ac9a3d0587bb1c98551@intel.com>
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

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