Fix zlib compression

While portions of the code needed to support z_compress_level() and
z_uncompress() where in place.  In reality the current implementation
was non-functional, it just was compilable.

The critical missing component was to setup a workspace for the
compress/uncompress stream structures to use.  A kmem_cache was
added for the workspace area because we require a large chunk
of memory.  This avoids to need to continually alloc/free this
memory and vmap() the pages which is very slow.  Several objects
will reside in the per-cpu kmem_cache making them quick to acquire
and release.  A further optimization would be to adjust the
implementation to additional ensure the memory is local to the cpu.
Currently that may not be the case.

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