- Introduce a specific function, pmap_remove_kernel_pde, for removing
   huge pages in the kernel's address space.  This works around several
   asserts from pmap_demote_pde_locked that did not apply and gave false
   warnings.

Discovered by:	pho
Reviewed by:	alc
Sponsored by:	EMC / Isilon Storage Division
Fix a panic in tmpaddrtimer.