regulator: tps65090: Poll timeout bit on enable

regulator: tps65090: Poll timeout bit on enable

Instead of just reading power good bit once, poll the register up to 5
times. This fixes an issue where the regulator is not setup and we read
the status too early. We will now wait until either the TOFET bit is
de-asserted, or ~5 ms elapse before checking for power good.

BUG=chrome-os-partner:12762
TEST=Tested on snow, no regressions found

Change-Id: Ied6dc840dcc4a94970cecac659efbffcbb55d651
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/31072
Reviewed-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Olof Johansson <olofj@chromium.org>