Allow ENABLE_ROLLBACK broadcast to be sent before boot complete.

This is needed in the case when we commit the apk session for a staged
session post reboot. The rollback manager registers its receiver early
enough that it will not miss the broadcast.

Bug: 112431924
Test: adb install-multi-package --staged --enable-rollback \
        com.android.tests.rollback.testapex.RollbackTestApexV2.apex \
        RollbackTestAppAv2.apk ; adb reboot

Change-Id: If070633d761ec673f1dd2753cbb359ca31e53b9c