Changeset 140

pmap_pv uses a spin lock so we can't sleep with this lock held.
Especially, make sure pv operations won't sleep on the pm_lock:

• pmap_map_ptes() gains a "wait" argument, if !wait use trylock and return error as appropriate.
• Deal with EAGAIN in pv operations by restarting the sequence.

Try harder to not return error in pmap_ctor() if we're allowed to
sleep.