tcpc: use initialization complete alert bit to signal readiness

Use the new TCPC initialization complete bit in alert register to
signal TCPC readiness instead of checking for USB VID to be set.

BUG=none
BRANCH=none
TEST=load on glados, make sure we can boot without battery.

Change-Id: I4b25c973ece0de6dd3f419c5901cff1d8d05ed95
Signed-off-by: Alec Berg <alecaberg@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/282593
Reviewed-by: Scott Collyer <scollyer@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
2 files changed