uts: enable very early console on ttyb
The boot loader will jump to dboot (which is 32-bit code to prepare the machine to be switched to 64-bit mode), and we are effectively blind (no output), till the console is set up.
Incidentally, we can try to use serial port till the real console is there, so at least there is some chance to catch some early messages - for case anything will go wrong that early.
Note, this early, we do not have any other resources, just our code.
We use ttyb since it is most likely there for systems with remote management.