Change pmap_demote_l2_locked() so that it removes the superpage mapping on
a demotion failure.  Otherwise, some callers to pmap_demote_l2_locked(),
such as pmap_protect(), may leave an incorrect mapping in place on a
demotion failure.

Change pmap_demote_l2_locked() so that it handles addresses that are not
superpage aligned.  Some callers to pmap_demote_l2_locked(), such as
pmap_protect(), may not pass a superpage aligned address.

Optimize TLB invalidation in pmap_remove_l2().

Change the arm64 pmap so that updates to the global count of wired pages
are not performed directly by the pmap.  Instead, they are performed by
vm_page_free_pages_toq().

Batch the TLB invalidations that are performed by pmap_protect() rather
than performing them one at a time.

Eliminate a redundant call to pmap_invalidate_page() from
pmap_ts_referenced().

Introduce pmap_remove_l3_range() and use it in two places: (1)
pmap_remove(), where it eliminates redundant TLB invalidations by
pmap_remove() and pmap_remove_l3(), and (2) pmap_enter_l2(), where it may
optimize the TLB invalidations by batching them.

Implement pmap_copy().

Three changes to pmap_enter():

1. Use _pmap_alloc_l3() instead of pmap_alloc_l3() in order to handle the
possibility that a superpage mapping for "va" was created while we slept.

2. Eliminate code for allocating kernel page table pages.  Kernel page
table pages are preallocated by pmap_growkernel().

3. Eliminate duplicated unlock operations when KERN_RESOURCE_SHORTAGE is
returned.