Allow update_verifier to write to kmsg

Denial message:
avc: denied { write } for pid=640 comm="update_verifier" name="kmsg"
dev="tmpfs" ino=13951 scontext=u:r:update_verifier:s0
tcontext=u:object_r:kmsg_device:s0 tclass=chr_file permissive=0

Bug: 64713327
Test: update_verifier logs successfully during boot time.
Change-Id: I421b1e6660239e5ffc624e504f5945d400510407