Consolidate all the information needed by the guest page table walker into
'struct vm_guest_paging'.

Check for canonical addressing in vmm_gla2gpa() and inject a protection
fault into the guest if a violation is detected.

If the page table walk is restarted in vmm_gla2gpa() then reset 'ptpphys' to
point to the root of the page tables.
Untabify.

Found by:	jmmv @
Add a new taskqueue setup method that takes a cpuid to pin the
taskqueue worker thread(s) to.

For now it isn't a taskqueue/taskthread error to fail to pin
to the given cpuid.

Thanks to rpaulo@, kib@ and jhb@ for feedback.

Tested:

* igb(4), with local RSS patches to pin taskqueues.

TODO:

* ask the doc team for help in documenting the new API call.
* add a taskqueue_start_threads_cpuset() method which takes
  a cpuset_t - but this may require a bunch of surgery to
  bring cpuset_t into scope.