WORK IN PROGRESS FOR COMMENTS cam_sim: create a list of sims, switch to smr and refcount(9)

[imp]

Summary

Link all the sims together in a list. To manage lifetimes, transition to
using smr for allocations and freeing. Transition to using refcounts for
lifetimes. Stop sleeping for the refcount to drop to 0, and instead
finish freeing the sim once the reference count drops to 0. It should be
safe to do so from all contexts we hold/release the sim.

Sponsored by: Netflix

Test Plan

This is a quick posting of code that's still a work in progress to allow discussions.

[imp]

Update sim_action and sim_poll to be 'dead' versions. This allows any CAM
requests to die gracefully once the sim has signalled it's done by calling
cam_sim_free(). Will update the commit message.

[imp]

I'm going to break this up into smaller steps.