Add C2000 KX and 2.5G.
Enable vnd and putter pseudo devices.
Use "-Os -m68020-60" for DBG. It seems to generate smaller objects than -Os.

gcc48 with "-Os":
-rwxr-xr-x  1 tsutsui  wheel  1319596 Nov 16 20:50 obj.atari/instbin

gcc48 with "-Os -m68020-60"
-rwxr-xr-x  1 tsutsui  wheel  1314516 Nov 16 20:49 obj.atari/instbin

This allows ever growing sysinst.fs still fit into 1440KB even with gcc48.
Acually we need a real solution (ustarfs based floppies etc.) soon
but we can work around at least for NetBSD 7.0.

Should be pulled up to netbsd-7 (if NetBSD/m68k 7.0 will switch to gcc48).
Set dependency via KERNLDSCRIPT.  Don't touch SYSTEM_DEP from outside.