I went ahead and switched the sun3x to MACHINE_NEW_NONCONTIG
after some testing last evening.  That means UVM is usable.

At this point, kernels with UVM appear to work on both the
sun3 and sun3x.  After some more testing the config files
will all be changed to make UVM the default.

Please try out kernels configured with "options UVM"
and send-pr any problems.  Thanks!

Oh yeah, there is already one known bug (PR#5239) that
UVM kernels seem to tickle when using nullfs mounts.
Apply the patch in that PR, or don't use nullfs...

Gordon