spring: Poll CABLE_DET for a second
spring: Poll CABLE_DET for a second

We've seen CABLE_DET being asserted hundreds of milliseconds after
ID_MUX is switched. To ensure video dongle is detected, let's poll
CABLE_DET for a second before declaring it an USB host.

BUG=chrome-os-partner:20405
TEST=Manual
BRANCH=Spring

Original-Change-Id: I1858f4075f526ee198b7b5f7ad2bb06cf6e3512c
Signed-off-by: Vic Yang <5fd92abeee651458f98e2856f4f200ee971cee4d@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/59887
Reviewed-by: Jeremy Thorpe <jeremyt@chromium.org>
(cherry picked from commit 2d37619a934264cf4f902078b081b76d607ddce1)

Change-Id: I55fba167780fb7e04157655dc5b3a2e76b8999c5
Signed-off-by: Vic Yang <5fd92abeee651458f98e2856f4f200ee971cee4d@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/60622
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

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