make the installation media's life easier:
- stop using ``Pc'' as a getty terminal type, use std.9600 instead.
- on platforms with multiple virtual consoles (alpha, amd64, i386,
zaurus), console is disabled, various ttyC* are enabled.
- on other platforms, console is enabled, all other devices are
disabled. This only changes armish, mac68k, sgi.
- default terminal for console is unknown on serial-only machines, vt220
on glass-capable machines (questionable, but done for consistency).
- minor whitespace changes.
- glass console forgotten on a couple platforms (luna88k, sparc64, vax).
eyeballed by deraadt@, ok krw@