[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.