spring: Fix S3 USB charging bug
spring: Fix S3 USB charging bug

The EC currently assumes the AP only provides USB power during S0, which
is incorrect. This CL adds S3 so that it behaves when the device is
suspended.

BUG=chrome-os-partner:19190
TEST=Suspend and unplug power. Doesn't hear clicking sound.
BRANCH=Spring

Change-Id: Ice1421bda55b2fee408ba062ed3de7a697ccd0c8
Signed-off-by: Vic Yang <5fd92abeee651458f98e2856f4f200ee971cee4d@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/50093
Reviewed-by: Todd Broch <035f5b1f817cbb94019cec357b99778115602b63@chromium.org>
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

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