ilo: replace cp hooks by cp owner and flush callback

ilo: replace cp hooks by cp owner and flush callback

The problem with cp hooks is that when we switch from 3D ring to 2D ring, and
when there are active queries, we will emit 3D commands to 2D ring because
the new-batch hook is called.

This commit introduces the idea of cp owner.  When the cp is flushed, or when
another owner takes place, the current owner is notified, giving it a chance
to emit whatever commands there need to be.  With this mechanism, we can
resume queries when the 3D pipeline owns the cp, and pause queries when it
loses the cp.  Ring switch will just work.

As we still need to know when the cp bo is reallocated, a flush callback is
added.