Add ueventd to mnt_vendor_file neverallow exemption list

Legacy hardware and code still depends on the ueventd helpers to
locate the firmware supported files which are on new mount path
labeled with mnt_vendot_file. For ueventd helper to work we need dir search
and read permission on this new label so moving ueventd to exempted list.

Already ueventd has the vendor_file_type read access.

Bug:110083808

Change-Id: Ia15cc39ecef9e29b4f1f684efdddbeb78b427988