Because we need to use a break-before-make sequence when promoting pages
there is a short period where functions that walk the kernel page table
without locking them may see an invalid entry. One solution would be to add
locking to these functions, however some may be called from locations where
we are unable to sleep.

Until a better solution can be found stop promoting pages in the kernel
pmap so these functions work as expected.

Obtained from: ABT Systems Ltd
MFC after: 1 month
Sponsored by: The FreeBSD Foundation