When running an N32 kernel, run it with 64-bit addresses even though the
kernel itself will only use 32-bit addresses.  There are exceptions.
bus_space_handles are now register_t instead of intptr_t.  This allows them
to contain XKPHYS addresses.  Now bus_space can use XKPHYS addresses and
not required non-KSEG1 devices to be mapped in KSEG2 thereby leaving more
KSEG2 space for the kernel to use.

The cache range routines (but not index routines) now take a register_t
instead of vaddr_t so they can too take a XKPHYS address.  This allows the
pmap to use a page's XKPHYS address to clean sync the icache thereby avoiding
massive icache invalidations.

Since "cache" instruction effects are global to all CPUs and their caches, we
can use the above to greatly simplify MP page isyncs.  If using an O32 kernel
with pages outside KSEG0, index ops still need to be performed since there
isn't an a quick way of mapping the page.

(matt)