Multiple virtual mappings considered harmful on ARM

[Mark Tinguely]

Looking at the pmap code real quick, I think the original authors
assumed quick kernel entries were not shared. Since they can be, we
should have to add pv_entrys and the cache vac/fix process on the
pmap_kenter_internal called routines too.

I am still thinking the ARM code should revolve to FreeBSD style
(recursive page tables, make SMP ready, etc).

--Mark.