init: Make console a shutdown critical service

A critical shutdown service is one that stays on right until the system
is rebooted. In order to be able to capture kernel messages right until
reboot this is required, otherwise after the console service is
terminated some messages can be lost.

Test: Reboot and verify messages show up on serial further down the reboot process
Change-Id: Iea58b5a76afe45b3346803021e3be81742b02ea0