Factor more console init into arch code

This allows architectures to skip specifying a console at all.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Rename virtme_stty_console to virtme_stty_con

Several architectures look for "console=" with strstr in the command
line, causing random breakage.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>