Treating all FileSection files as device specific.

Arc++ devices don't have the /d/wakeup_sources file. There's a chance
other device won't have it either, and there may be other files that we
thought were standard but are actually not, so it's safer to just assume
that not every file will be available on every device and not treat a
missing file as an error.

Bug: 110109543
Test: atest incidentd_test
Change-Id: Ief09427f08d18aee611d057ddafdb9a3466744db