Make code match comment: make the smallest unit of page allocation from OpenFirmware be 16 pages to avoid fragmentation in the list of mappings returned when the kernel requests it in pmap_bootstrap.
Make code match comment: make the smallest unit of page allocation
from OpenFirmware be 16 pages to avoid fragmentation in the list
of mappings returned when the kernel requests it in pmap_bootstrap.

This allows a static buffer to be used when obtaining the existing
mappings - very useful on the G5 when random physical pages can't
be grabbed because they can't be BAT-mapped.

MFC after:	3 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase