sysisnt disallowing FFSv2 (patch)

Hi,

We have a flag to disallow making a FFSv2 root filesystem. I assume this
exists because shark's bootloader can do FFSv1 but not v2. I am
proposing changing the polarity of this macro.

The default filesystem choice is controlled by another macro, DEFAULT_UFS2
(used by x86, sparc64).

Here is a diff (not attached, since it mostly rotates flags per arch):
http://coypu.sdf.org/sysinst.diff

Functionally changes sysinst for the following archs:
acorn26, amiga, atari, bebox, cats, dummy, evbmips, evbppc, evbsh3,
ews4800mips, hp300, hpcarm, hpcmips, hpcsh, luna68k, mac68k, mipsco,
mvme68k, news68k, newsmips, ofppc, playstation2, prep, vax

Built & tested evbmips LOONGSON INSTALL kernel.

OK?