{Event,Security}Log: Unify code

Extract common code into eventlog_helper.

Bug: 67511924
Test: m
Test: Device boots
Test: cts-tradefed run commandAndExit cts -m CtsUtilTestCases -t android.util.cts.EventLogTest
Change-Id: Idafad832385f57c22f40dbb8570e95da6d44f08f
3 files changed