sys_util: add debug to eventfd
sys_util: add debug to eventfd

BUG=None
TEST=build

Change-Id: I37a19b56876a5b24caca413d33fde8330b12b187
Reviewed-on: https://chromium-review.googlesource.com/1327514
Commit-Ready: ChromeOS CL Exonerator Bot <fa429e5907f00867f797423aea74327bb02c91b6@appspot.gserviceaccount.com>
Tested-by: Jingkui Wang <c645f91f31b7cead6dc73127db4670945d892e95@google.com>
Reviewed-by: David Tolnay <1480464b87745a0822a0e8b7545ca981d8e7352e@chromium.org>
Reviewed-by: Zach Reizner <3374927928a53d04457674c546bd4de57c2044ec@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm