kernel - VM rework part 8 - Precursor work for terminal pv_entry removal
* Adjust structures so the pmap code can iterate backing_ba's with
just the vm_object spinlock.
Add a ba.pmap back-pointer.
Move entry->start and entry->end into the ba (ba.start, ba.end).
This is replicative of the base entry->ba.start and entry->ba.end,
but local modifications are locked by individual objects to allow
pmap ops to just look at backing ba's iterated via the object.
Remove the entry->map back-pointer.
Remove the ba.entry_base back-pointer.
* ba.offset is now an absolute offset and not additive. Adjust all code
that calculates and uses ba.offset (fortunately it is all concentrated
in vm_map.c and vm_fault.c).
* Refactor ba.start/offset/end modificatons to be atomic with
the necessary spin-locks to allow the pmap code to safely iterate
the vm_map_backing list for a vm_object.
* Test VM system with full synth run.
UnifiedSplitRaw
