MFC: r205399

MFC: r205399

Improve the KVA space sizing of r186682; on machines with large dTLBs we
can actually use all of the available lockable entries of the tiny dTLB
for the kernel TSB. With this change the KVA space sizing happens to be
more in line with the MI one so up to at least 24GB machines KVA doesn't
need to be limited manually. This is just another stopgap though, the
real solution is to take advantage of ASI_ATOMIC_QUAD_LDD_PHYS on CPUs
providing it so we don't need to lock the kernel TSB pages into the dTLB
in the first place.

git-svn-id: svn://svn.freebsd.org/base/stable/8@206013 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f