Start serial console at the 'init' trigger

Start the serial console at the 'init' trigger instead of much later
when property triggers happen.  This will help debugging early boot
issues.

Test: serial console starts early for a userdebug build
Test: serial console still doesn't start on a user build
Change-Id: I7112a8e7171c9fa865c8787c9a3d14515bc59478