Auditing init and ueventd access to chr device files.

It seems likely that there is no reason to keep around a number of
devices that are configured to be included into the pixel kernels. Init
and ueventd should be the only processes with r/w access to these
devices, so auditallow rules have been added to ensure that they aren't
actually used.

/dev/keychord was given its own type since it's one of the few character
devices that's actually legitimately used and would cause log spam in
the auditallow otherwise.

Bug: 33347297
Test: The phone boots without any apparent log spam.

Change-Id: I3dd9557df8a9218b8c802e33ff549d15849216fb