Make prefaulting more aggressive on hard faults.  Previously, we would only
map a fraction of the pages that were fetched by vm_pager_get_pages() from
secondary storage.  Now, we map them all in order to avoid future soft
faults.  This effect is most evident when a memory-mapped file is accessed
sequentially.  Previously, there were 6 soft faults for every hard fault.
Now, these soft faults are eliminated.

Sponsored by:	EMC / Isilon Storage Division
Add driver for Display Control Unit (DCU4).