From: William Lee Irwin III <wli@holomorphy.com>

->valid_addr_bitmap is initialized nowhere.  Any kern_addr_valid() testing
it returns 0 unconditionally.

This patch converts kern_addr_valid() implementations using it to return 0
as per the above and removes it from structures and zone initialization.
Untested (not even compiletested), though a similar patch also nuking
d_validate() was in use in -wli for several months.