Allow the user tsb to span multiple pages. Make the default 2 pages for now

until we do some testing to see what's best.  This gives a massive reduction
in system time for processes with a relatively large working set.  The size
of the tsb directly affects the rss size that a user process can keep mapped.
When it starts to get full replacements occur and the process takes a lot of
soft vm faults.  Increasing the default from 1 page to 2 gives the following
before and after numbers for compiling vfs_bio.c:

before:
       14.27 real         6.56 user         5.69 sys
after:
        8.57 real         6.11 user         1.62 sys

This should make self hosted builds more tolerable.

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