[dm-cache] protect mq policies residency method with a mutex.

It is safe at this point since only called from ioctl context.
whitespace
[dm-cache] io destined for the cache device can now be tick bios

Previously only origin bios could trigger ticks, which meant if all
the io was destined for the cache no ticks were generated.

Only a stop gap fix, we need a better solution.
[dm-cache] Fix bug in growing dm-arrays.

Entries would be lost if the old tail block was partially filled.
[dm-cache] mq policy should assume new entries are clean.

The core target initialises it's dirty bitset to clean, so we want to
agree.
[dm-cache] fix a race condition between queuing new migrations and quiescing for a shutdown.

The code that was trying to do this was inadequate.  The postsuspend
method (in ioctl context), needs to wait for the worker thread to
acknowledge the request to quiesce.  Otherwise the migration count may
drop to zero temporarily before the worker thread realises we're
quiescing.  In this case the target will be taken down, but the worker
thread may have issued a new migration, which will cause an oops when
it completes.
[dm-cache] Make the quiescing flag an atomic_t and stop protecting it with a spin lock.
Merge Mike's tree
delete + files
[dm-cache-policy-era] remove debug messages that we won't get upstream anyway.
[dm-cache] Fix a couple of ERR_PTR errors when creating policies.
[dm-cache] only run invalidations if we're not quiescing the target.
[dm-cache] update to Heinz' latest invalidate_mappings
[dm-cache] Add separate policy method to get the count of config arguments.

Now we're stacking policies we can't let them emit their own counts.
[dm-cache] more vacillating on the PTR_ERR stuff
[dm-cache] switch to using an atomic_t for era policy.  Era's now start at 0.
[dm-cache] Change era policy to handle all map results from the child policy.

We have to do this to avoid issues when recovering from a crash.
[dm-cache] rename some variables in the era policy
[dm-cache] tidy era_load_mapping
[dm-cache] era fluff