Defaulting WSCONS in NetBSD/amiga GENERIC

[David Brownlee <abs%absd.org@localhost>]

Are there any remaining Amiga configurations supported by GENERIC but
not WSCONS (in as far as being able to run a text console and wsfb
X11)?

If not, it feels like time to default NetBSD/amiga GENERIC to WSCONS enabled

So, proposal
- Enable WSCONS in amiga GENERIC
- Add a NO_WSCONS kernel for now as a fallback
- Look at adjusting X11 to default to expecting wskbd (similar to other ports)

I think adding wscons=YES and enabling ttyE0-E3 in /etc/ttys should
rightfully be part of sysinst, and the miniroot should include
sysinst, but that is a separate phase

David