elog: Add events for USB2.0/3.0 wake

BUG=b:37088992
BRANCH=None
TEST=Verified that wake source shows correctly:
19 | 2017-06-08 15:43:30 | Wake Source | PME - XHCI (USB 2.0 port) | 3

Change-Id: I0068fa227cd36bbd0761f046f3b1d5497bb46da4
Signed-off-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/528311
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
2 files changed